Are you using a sub? Is your listening mostly HT/TV or do you also listen to a lot of music (2 channel stereo)?
If you're using a sub (or sub's) and listening primarily to HT/TV the Q300's will fill the room fine. It might be worth noting that a third Q300 as a center would give you an excellent, even front soundstage. (Another pair of Q300's is actually a bit cheaper than a Q600. And because it's a concentric speaker you can lay it on it's side if you need to for space reasons.)
If you listen to a lot of 2 channel stereo music I would agree that you should consider towers for LR fronts in a room that size.
I haven't heard the Focals but they get universally good reviews, and that special pricing on A4L is a rare deal.