Optimum speaker height for home theater.

Mitch that sounds like a great room if you place the speakers and set the delay correctly. It will be cool to see pics on your system when you get it all up and running....good luck

Movie theatre speaker setups have nothing to do with good sound. The side speakers are up high so that when the theatre is full, the people on the edges don't block the sound for the people in the middle. It just helps with dispersion. It's also why nuclear weapons work best when they explode above the gound rather than at ground level, although I don't know why I just thought of that.

Another thing that theatres do is pump up the volume in the centre dialog speaker so that people on the side don't get blasted with sound from side speakers. You end up with theatre sound that's closer to mono.

Ear level is best because higher frequencies are more directional. However, original surround sound was primarily for low frequency effects. A high location for the speaker doesn't matter because the low frequncies are not very directional. You get the effect no matter where the speaker is. For discrete surround, the practicalities mentioned above take precedence over the niceties of good sound reproduction. High mounted speakers also keep kids from from shoving fingers through speaker cones or stuffing garbage in speaker ports.

"I plan to go to a 9.1 setup. All of the surround speakers will be full-range Infinity Kappa 9. The surrounds will not be used for music at all....only for home theater.

The Kappa 9 are 5ft tall. I was considering mounting them at 10ft off the floor (my ceiling is 22ft high)." (mitch4t)

A few issues come to mind when I think about your considerations here, and it all leads to BALANCE! First, you MUST deal with some sort of system equalization or DSP room correction, and I recommend bass managment!(even for larger speakers, like the Kappa's). Basically, the speakers are going to be on/near the walls, and bass modes will need to be dealt with, as well as smoothing out the bass hump/boom that will be pressent near the room boundaries, when you place speakers there.
Another consideration is the "speaker aim" and "comb-filtering" from driver to driver, in relation to the seating possitions! You will likely encounter some response filtering, if your speakers aren't "aimed" at the seating possitions, largely. You can experience this phenominon by simply playing a speaker on the floor, and ducking down, or standing above the speaker, and listen for "roll-off", "holes in the sound", "tonality change", etc! This is a factor, for sure. that's why more wide dispersion, dedicated rears, even dipoles are often effective, in part. Dirrect radiators often are more "beamy" in pressentation. So those would be SOME of the concerns I would want to adress, if it were my system
Also, yes, even though those speakers may be more full range, I'd cross em over higher, get WAY more effeciency out of em, and enlist plenty of worthy subwoofers into the system! (this is another issue to deal with entirely).
Also, setting delays for the surrounds might be a bit tricky, depending on how you set the speakers up in relation to the seating arrangement. You migh consult the "pro audio forums" or info on cinema speaker set-up's, and dig around to see what they're doing for multiple surround arrays, delays, eq'ing, etc.
For me, it's ALWAYS quality before quantity! But, yes, balance, is necessary.
Good luck