Hi Lakefront:
I've heard a few and unfortunately it's not mine at the moment. I thought I would throw out one short thought.
The idea of an "ideal room" seems a little problematic to me. Sound includes direct sound and sound due to resonances, reverberation, reflections.. as you know. Seems like the speakers you use and their characteristics will have a big impact on how these interact in a room.
If you just look at one thing, like the off-axis radiation pattern of a specific speaker, it's not hard to see that different speakers will act differently in the same room. If you put a typical box, large panel area dipole, or open baffle ....ect ect...in a room it seems that a room that deals best with one might not be so hot with the other.
Have you thought about bringing a pro in? Talk to Albert Porter (I think it's Albert Porter) who posts here. I think he is in the middle of such a project.
Also, I'm sure Kirk's room was great but general advice would be to avoid creating dimensions that are even multiples or fractions such as 20/30.
Just found a fun Room Mode calculator on line at www.mcsquared.com/modecalc.htm which is kind of fun.
Just a thought. Have fun!
I remain,