leave crossfire to the highest end cards when you need more performance than the fastest single card available. Stick to a single better card and avoid microstuttering, trust me, i know. Going to sell my 6850's because of microstuttering. It's not always noticeable, and there are workarounds but they are fiddly and leave you with a lower average fps, but when you see mirostuttering, games become more unplayable than just dealing with lower fps.
I'm ironically running a 7870 and 7850 crossfired (due to price drops on the 7870), so far it runs very well on the games I've played, WoW, Sleeping Dogs, BF3 (works the best on BF3). I got the 7850 first and my logic behind getting a 7870 for the second card was for any games that do not support crossfire, the 7870 is a stronger card and I'd get more fps from it it. So far my system handles just about anything I throw at it (which these days isn't too much besides WoW with friends due to an erratic work schedule and school)(Plus I didn't really enjoy BF3 multiplayer unfortunately).
I did have an issue running The Secret World back when it was new and I was still using 12.3 drivers. I am now using 12.10 but have not tried playing the game again yet. (It had a bunch of graphical errors when I ran it, granted the game came out after 12.3 drivers, so its not surprising)
As to microstuttering, if I have it, I haven't even noticed it (keeping in mind I haven't got a point of comparison, so its possible I just don't know what to look for). My games run pretty much 100% maxed out at 1080p at 50+ fps (usually 60 with vsync).
I'm running them with a 1055t @ 3.8 GHz and 16 GB of ram.