IMHO, it's not just theory on paper that says the QS's are good on the side, it truly does bear itself out in real world listening and comparisons.
I wouldn't bother trying the QS8's on the columns again. If you've tried them there before and didn't like it then it's not likely to sound any better this time around, mainly because you'd still be missing two back speakers. My vote for QS's on the columns was assuming you had two surround back speakers as well, now THAT would be a worthwhile test for you to do.
Bumping of heads and other mitigating factors are another thing. We all need to work with what we have, so if QS8's protrude out too much then you would need to look at the smaller QS4 or other in/on wall models instead.
