Interesting. I was going to start a thread on exactly the same subject today!
I have the 601 s3's and a REL Q100E which I use mostly for music (having sold an LCR600 and run out of money before falling for the 603's, lol). While they sound absolutely stunning, seriously exceeding my expectations despite a great demo and 5/5 reviews all over the place, next year I could be back in a dorm and might switch to a pair of 600's and a modest amp (NAD c320 or something similar).
I have never heard them, but would presume they are similar in character to the 601's (rear-ported though, right?). Being very neutral speakers as it is, I'm sure that upon first impression they will seem somewhat lacking in low-end (only a 12-13cm mid/bass driver, I think) but for the size probably can't be beaten. In fact I think it's nice that B&W didn't try to force the low-end on such a small unit. Of course, well-integrated with a decent sub in a small room they'll shine. You might find them slightly "monitor-like" though, not that that's a bad thing in many people's eyes.
It's probably best you go and have a listen. Bear in mind that they really, really improve when fully run in. Some people reckon 100 hours at least for the 600's and while that might be a slight exagerration it can't be far off. Nice little speakers, although you might want to consider 4 plus an LCR60 for centre duties.
MuFu.