I had a chance to perform a direct comparison between the Bryston 2.5B3 and a Pass Labs amp (I forget the model) in the same setup. They simply sound different so I believe it will really come down to which you prefer. I prefer the Bryston, but the other person who was with me prefers the Pass.
I have also compared the newer Bryston cubed amps to their previous generations and there is also a very noticeable difference in sound character. So I wouldn't necessarily take the 135SST as a good reference point if you are considering the 4B3. I prefer the newer cubed series, but I have met people who prefer the older models after performing direct comparisons.
