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

I hope you don't mind that I answer your question indirectly, but I have some advice and recommendations that I feel are beneficial for your particular situation:

Consider using the Lyngdorf RP-1 digital sound processor.
This unit uses advanced eq to correct uneven response from speakers in less-than-ideal situations. Considering the equipment you use, I guess you might be apprehensive about inserting a digital processor into the middle of your audio chain, but I'm pretty sure you'd be far happier with the RP-1 than without it.
review: http://www.dagogo.com/Lyngdorf-RP1.html

You should read Cardas Audio's article on speaker placement in square rooms: http://www.cardas.com/content.php?area=insights&content_id=33&pagestring=Room+Setup+8

Consider room treatments, especially bass traps.

As far as reference quality, top of the line, small-room-friendly speakers go, you may want to audition the following: Magico Mini II, Merlin TSM-MMe/MXe, AAD 7001i, Usher BE718, and possibly the Silverline SR17.5.

If you crave the deep, powerful bass that bookshelf speakers can't provide (even in small rooms), a pair of subwoofers would sound more balanced than only one. I read that the Axiom EP400 subwoofer (8" sealed) is more articulate than the JL Audio Fathom F113 (13" sealed), although the former doesn't go as deep or hit nearly as hard as the latter. Regardless, I suspect that the 10" JL Audio Fathom F110 is just as articulate as the Axiom EP400. For ultimate speed and accuracy (and price) the Wilson Benesch Torus is another good option, although it hardly provides half the slam of the Fathoms and it takes up more space. Of course, the Lyngdorf RP-1 would allow you to seamlessly integrate any of these subwoofers into your system.

I hope I've helped.

Ohm Micro Walsh talls. I have a 11X11' room with 9'ceilings and it sounds amazing. It's all the speaker that you'll ever need for a room that size

No doubt I'd put a pair of OHM Micro Walsh Talls in there, build around that and be done. They are explicitly designed to go into small rooms in particular.

I use slightly larger OHM Walsh 2s with OHM Walsh 100 series 3 drivers in a 12X12 room. These work to the max in the room, but I suspect smaller and less expensive MWTs (or their shorter brothers, the Micro Walsh Shorts in some cases) would suffice.

it is only the bass response of the speaker that will cause problems, so if you're willing to do either of the following, it will greatly expand your options and ability to get a larger speaker to sound good in that room:
1) room treatments (bass traps in corners, all the way to the ceiling)
2) Rives Audio PARC (an eq for bass frequencies) or similar type product (Tact, etc)

if your budget is flexible, buy a larger speaker & have the room measured after setting up. determine where the nodes are, and address using either 1 or 2 above. the PARC is quite flexible and will remove room nodes where you have too much bass by targeting specific frequencies.

you will have too much bass in that room unless you address it. just dont be a passive victim; work for good sound, and you can definitely get it, using full size speakers in there.

(my room is 11*15 and i use Wilson WPs in it w/ no trouble, but take a look at my system pics---room treatments everywhere. if i did not have the ability to have room treatments everywhere, i'd have the PARC. if i had neither, it would sound terrible, which i know from experience).

I have a very vanilla 12X12X8 office/listening room. Concrete foundation with thin carpeting, drywall, typical office furnishings including couch to listen from (photo in my system posting).

Ive tried B&W floorstanders, Maggies, Triangle and Dynaudio monitors, and large and small OHM Walshes in that room.

The smaller full range OHMs currently there work best both in terms of sound quality and overall utility in a small/cramped room, followed by in descending order of fit Dynaudio or Triangle monitors, Maggies, B&W floorstanders (P6s)and lastly big OHMs (just too big for such a small room though they sound great).