My room is very similar to yours, size-wise. Mine is about 22' wide 14' front to back, 8' ceiling, and opens to a staircase and 4' wide hallway that leads down about 15 feet. It's all finished drywall on metal studs and concrete block, with carpet over concrete floor.
I've got the Velodyne SPL-1200 II and am still breaking it in, but so far I am very very pleased with how this sub reaches down low and fills the room with bass. With the system calibrated with YPAO on my Yamaha RX-V2500 and the sub set at "2" - the Yamaha indicates -2.5 dB for the sub level. Naturally, I crank the sub up to about "4" to suit my bass-head requirements, and I have plenty of room for adjustment.
The fit and finish on the Velodyne is superb. I got the "black" one, but it's really a very dark shade of translucent blue over maple. You can see the wood grain through the finish, and it looks fabulous. The sub looks great with or without the grille - seeing that 2" cone excursion during heavy scenes is really cool. =)
For me, the deciding factor to go with the 12" over the 10" was to get the extra 2 Hz of low-end response, and slightly greater headroom for when I really want to crank it up. No doubt you can save some cash going with the 10" and the SPL-1000 II would probably fill your room with enough bass... but you'd be at 24-120 Hz +/- 3 dB instead of 22-120 Hz.
Greg