I have pretty much the same kind of set-up that you do, but my room is 12 x 12. I just purchased the M60's and next month plan to get the VP150 and QS-4's. I am going with the QS-4's for two reasons. A) My receiver is 80W and B) I don't listen at high volumes.
Since my receiver's crossover is at 80Hz, it pretty much levels the playing field between the two. The QS-4 goes down to 75Hz and the QS-8's to 60Hz- but that is negated with the 80Hz crossover. So them it comes down to volume level. If you play at high volumes with a high powered amp, then the QS-8's would be best. If you're like me who plays at normal volumes with a mid-powered amp, then the QS-4's would be more than adequate.
Just my thoughts on the subject. :-)
-Brad
