how big a speaker can you put in an 11 x 11 room?

Will you be able to place the speakers properly away from the walls and still sit far enough away from them for the separate drivers to cohere? You can't sit but so close to physically large multi-driver systems and not hear the individual drivers as individuals drivers.

I'm not even going to mention that your room is a square and the problems that will present for smooth bass response.

Search the forums for threads on speakers that work well when placed directly against the wall.