green mountains

I will let others with more experience with Green Mountains give their impressions. This was my first real audiophile speaker.
The way I understand it, first order crossover speakers are more crucial to place correctly, and have a smaller sweetspot. I may be wrong on that.
I think if you want better feedback you should list what kind of music you listen to, what kind of spl levels you listen to, room size, amp to be used, and if you plan on running a subwoofer.
If you love the sound of your speakers, maybe moving up the line is great move for you.
I just think there are many great options for monitors for under $2500 especially when you are considering buying used.

I have not heard the particular speakers you asked about, but I have heard and owned quite a few of Roy's designs.

Once you hear time and phase coherency done right, it's hard to go back to anything else. I currently have the Continuum 3 HDs and I believe them to be fantastic speakers. I don't think there is anything that I could afford that can beat them. Something will, for sure, but it's probably out of my reach.

As mentioned earlier, give Roy a call. He is always ready to talk about his speakers.

Shakey

I haven't heard the Rios or Europas, but I owned a pair of Pico Executive HDs last year. They throw a very nice, detailed 3-D soundstage with excellent pinpoint imaging. Tonal richness and timbral accuracy is fantastic, and the sound is very smooth, pleasant and engaging.

The phase-coherent design I also liked, and I think it helped enhance the front-to-back dimensionality of the presentation. I didn't think they were any more susceptible to a small sweet spot than lots of other speakers - perfectly easy to enjoy them while sitting in a chair off to the side.

That said, the imaging and soundstage are liable to be on the smaller side. The GMA designs generally don't provide a lot of bass and aren't the last word when it comes to dynamics. They're certainly not below-average, either, but I think they lean more toward sounding smooth and beautiful, as opposed to "live" and "exciting." Mind you, I imagine that could change with a more powerful amp than what I was using.

as a previous owner of a pair of Green Mountain C1.5i my impression of Green Mtn's products is that they are very, very good products. I liked my C1.5i very much in every regard w.r.t. its sonic characteristics. I had a powerful enough amp such that the C1.5i sounded live & exciting. I quite diagree with Cfluxa's view of his speakers sounding "more toward sounding smooth and beautiful, as opposed to "live" and "exciting" but he did add "Mind you, I imagine that could change with a more powerful amp than what I was using" & I believe that was his problem.
Besides owning the C1.5i, I've heard the Calisto 2-way in the factory + at my brother's house (he owns a pair).

like another member posted, Roy is an excellent person to talk to - very knowledgeable & very humble & like it was written before, very giving of his time. Give him a call & ask him all the tough (& I mean really tough) questions you have about his products. That's what I did before I bought my C1.5i - hrs were spent on the phone asking Roy questions about speaker design & how he approached the matter. It became quickly apparent that Roy was a goldmine of info - he actually reads the IEEE AES papers & tries to apply the info in there to his speaker design - and that he could answer my questions directly w/o beating around the bush. I learnt that his choices for material, speaker drivers, hook-up, type of glue, type of screws was all very deliberate; nothing was merely coincidental in the hardware used.

I was initially drawn to the Green mountains because of the advertised claims of time coherency which other speakers do not have. What can you say about this? Are there any qualities which are audible with GMA that are lacking in others?

Roy advertises his speakers to be time-aligned & phase coherent & there is no gimick in his statement - they are exactly what he says they are from my own experience. A phase coherent speaker is time-aligned but a time-aligned speaker is not necessarily phase coherent.
There are several other examples of time-aligned speakers such as (the now defunct) Meadowlark, Thiel. JM Lab (by making the baffle C-shaped), Dynaudio (by putting the tweeter at the bottom & the woofer on top). While all these speakers might sound great (I've heard a few of them) they are not phase coherent.
When you listen to Green Mountain speakers the 1st thing you notice is that the entire music sounds like it's cut from the same piece of cloth - there is no separate tweeter-separate-woofer effect. Also, there is no boxiness to the deep bass - the deep bass seems to be omni-present & does not seem to come from any direction; the deep bass is felt & not heard. My C1.5i went down to 44Hz so I was missing the final octave so the deep bass I'm talking about is 44Hz-80Hz. At the same time, what I found was that the mid-bass had superb tonality - I'm talking about the stand-up bass instrument where I could hear each string as it was plucked. A great test for this (for me) was track 11 from Diana Krall's "Love Scenes" CD - My Love Is. The 1st 45 seconds - can a speaker delineate that bass clearly - 'cuz the artist sure as hell is plucking each string separately but in quick succession - without muddying the bass. Muddying occurs if the woofer driver cannot start/stop quickly & you get bass overhang. The C1.5i was a sealed box bass (which I loved -w-a-y- more than any ported design I've heard even to-date) so the bass response was simply superb - just enough, not too much, not too little (like Goldilocks right). I have to agree with Cfluxa that the bass response can be light if you do not have a strong enough amp. Roy admitted that the sealed box was 1 of the reasons that the amp had to "kick" the woofer a bit harder. In my particular case I was using TARA Labs Master Gen II speaker cables & when I switched to Virtual Dynamics Nite II speaker cables, the bass response took a major leap towards the better in terms of quantity without losing the quality.
Also note that Green Mountain Audio are true 1st-order speakers i.e. they are electrically & acoustically 1st-order x-over designs. A lot of other speaker manuf use 1-st order x-over electronics but when they add this x-over to the speaker drivers the overall response becomes 2nd order because the 1st order x-over + the 1st order roll-off response of the speaker driver add together to make a overall 2nd order response. Not so with Green Mountain Audio speakers - the driver response is flat beyond the x-over frequency meaning that it's the 1st-order x-over making the speaker freq response 1st-order. The down-side to this is that you cannot play the speaker at ear-bleeding levels - the max SPL for the C1.5i was 105dB, which si very loud for home listening. If you want ear bleeding levels (like at an U2 concert) then look at other speaker manuf.
Roy shared with me some of the impedance & phase plots of his speakers (these are not published but the performance is written in words in the speaker spec sheet). I could see that the impedance response & the corresponding phase response were practically flat 200Hz - 8 to 10 KHz. Beyond this range on either side, the speakers had something like +/- 10 degrees of phase shift. This is the phase coherence of the speaker - the speaker itself contributes very little towards adding more distortion to the music signal & that's why the music sounds right & like music. There are very few speakers in the market that do this.
W.r.t. a speaker's output, lack of phase distortion is key. Always remember that, in Nature, phase is the independent variable & that frequency is the derivative of phase. If your phase response is flat, your impedance response will be flat as well.
This where the 1st-order x-over comes into play. The 1st order x-over is the only x-over response that keeps the group delay of all the frequencies flat i.e. all frequencies within the frequency band (in-band) are constant (rather than being variable like most other speakers in the market). Another way of saying this is that the phase distortion of Green Mountain speakers is very low. Other speakers that compete with Green Mountain Audio in this regard are the Quad ESLs, Apogee ribbon speakers and SoundLab ESL speakers to name a few. You can see what I'm implying here - the Green Mtn Audio speakers have a tonality & freq response that is much akin to an ESL speaker. Not an easy feat to achieve with cone dynamic drivers......
Hope that this info helps.
The best would be to give Roy a call & ask him a lot of questions that are swimming in your mind.

The most important aspect of GMA speakers to me is that they sound more like performers in your room, than a just a good pair of speakers playing music in your room. Exciting is exactly how I would describe them. And bass response is world class when you move up to the flagship. The monitors will give you sufficient bass for what they are.

Shakey