Read Hardware Canucks conclusion. It says what quite a few people are saying.
"Luckily for NVIDIA, we didn’t stop at the average framerates and included (as usual) minimums as well. In this category the GTX 470 SLI is still head and shoulders above the competition when IQ settings are pushed since it doesn’t exhibit the numerous dips in performance that characterize the Crossfire experience. I don’t know about you but I would much rather have a slightly lower average framerates if it means my system won’t bog down when I’m fighting for my life in a game. Basically, a fluid gaming experience is what SLI is ideal for…or at least until ATI can figure out a way to bring up their minimum framerates in some games."
For people that care about strong mins overclocked 470 SLi is going to turn out to be a winner. Yes that reviewer did praise 5850 Crossfire and he also mentioned it having more harsh FPS dips and lower mins. Again, IMO 34/55 is more desirable than 20/70.