It would save $ on speakers and amps to do a 5.1 system. For audio it will make no difference because the current selection of recordings, even SACD, are generally limited to 5.1 as far as I know.
I'd suggest that if you decide on a 7.1 system that you use a small and inexpensive pair of dipoles for rear surrounds. Missiion 77ds comes to mind because they add an extra dimension of realism to movie soundtracks that have been recorded in 6.1. They can be picked up for about $200 or less if you're good with Google, and since they are samll, triangular and white, they can be ceiling mounted to blend in. There is not much advantage to the 7th channel because the 6th and 7th channels simply split the same signal in two. For action movies, say in a scene where gunfire is coming at you from 360 dgrees, the extra channels produce some interesting effects, but you don't need heavyweight speakers with deep bass.
So to answer your question - no, your room is not too small for 7.1 if HT is important to you and you use samll dipole speakers. The practical differences between 5.1 and 7.1 are minimal, but certainly enjoyable. The surrounds should be placed immediately to the left and right of your listening position and the rear surrounds should be placed several feet behind and above your listening position to best achieve the seperation necessary to notice the effects described above.
I'd suggest that if you decide on a 7.1 system that you use a small and inexpensive pair of dipoles for rear surrounds. Missiion 77ds comes to mind because they add an extra dimension of realism to movie soundtracks that have been recorded in 6.1. They can be picked up for about $200 or less if you're good with Google, and since they are samll, triangular and white, they can be ceiling mounted to blend in. There is not much advantage to the 7th channel because the 6th and 7th channels simply split the same signal in two. For action movies, say in a scene where gunfire is coming at you from 360 dgrees, the extra channels produce some interesting effects, but you don't need heavyweight speakers with deep bass.
So to answer your question - no, your room is not too small for 7.1 if HT is important to you and you use samll dipole speakers. The practical differences between 5.1 and 7.1 are minimal, but certainly enjoyable. The surrounds should be placed immediately to the left and right of your listening position and the rear surrounds should be placed several feet behind and above your listening position to best achieve the seperation necessary to notice the effects described above.