i think a call to JR or RV is good. I have owned 5a and now 7 and Treo CT, so perhaps you might call me biased.
your room is not an issue, especially ceiling height- Vandersteen engineers the tweeter height to be remarkably similar across the line...for a reason!!!! your floor is treated :-) w carpet...maybe add some natural diffusers....but the big virtue is powered bass and 11 bands of analog eq. the tweeter on the CT is better than the 5a
the subwoofer on the 5a is better....
competently setup w good source I would call it a draw. smaller rooms favor the Q
now if you are guying new, get the Quattro, pick your wood or automotive finish AND enjoy the ocassional upgrade opportunity as an origional owner...