The simple answer is about what Newbee said. It's really more practical, in most applications, to use smaller speakers and maybe a well placed sub(Preferably EQ'd!).
Big speakers with deeper bass extension will tend to make it harder for you to get anything but bass heavy, thick, slow, boomy, "one-notey" bass, basically not smooth, flat and natrual. Small room already are heavily challenged acoustically, especially in the bass region! Putting large speakrs in there makes things tha tmuch more boomy, "unatural", "one-notey", and just plain "small room" "boom box sounding!".
Your only hope with even modest sized speakers in that room,complicated by the fact you're going to have to be near the back wall(depending on setup, but no much room either way) seat-wise, and your speaker are forced out in the room to try to smooth and even out your bass for natural sound and dynamic range.
One alternative here to making large speakers work in large rooms (like what is even comon with the small room setups at CES and other Hifi shows), is to use a good Parametric EQ on the speakers! Your basic choices are limited to either a good high end expensive parametric like Rives audio makes (see Stereophile, and or do research, even on this site), or use a basic Parametric on the bass drivers and bi-amp! This is an option on some speakers that sound good bi-amped (some don't!). IF you can EQ the bass on a speaker while leaving the other fundamentals (mid/trebble) intact, you can get some potentially stelar results with good set up and acoustical considerations in small rooms indeed! It's just a lot harder than it is for large rooms!
Still, for most, I'd recommend against large speakers in small rooms, unless you know what you're doing...most don't
