GTX 470 SLI setup is at least comparable to 5870 CF in performance. If you look at the minimum framerates though, 470 SLI is the preferable setup. When 470 SLI wins, it wins
big. There is hardly any time (Resident Evil 5) where CF wins convincingly:
http://www.xbitlabs.com/articles/video/display/geforce-gtx480-sli_6.html#sect1
This is why I have been recommending 470 SLI over 5870 CF for a while. But again from a noise and power consumption perspective, the CF setup can still appealing.
For single monitor setups, maybe. For multiple monitors, maybe not.
The HD5870 typically closes the gap single card vs single card as resolution increases (not always the case, but typical).
When it comes to multiple cards:
In Dirt 2, HAWX, AvP, CoD:MW2, Wolfenstein the gap closes between HD5870 and GTX470 SLI between 1680x1050 and 2560x1600
In BFBC2, Crysis, Metro 2033, Stalker, SF4, Mass Effect 2 the gap remains about the same.
In Battleforge, WIC, Far Cry, Just Cause 2, Resident Evil 5 the GTX470 SLI increases its lead.
So that's 5 to ATI, 6 neutral and 5 to NV from 1680x1050 -> 2560x1600 (winning based only on the change in gap and not who is faster overall. ATI could 'win' and still be slower, and so could NV, for example by going from being 50% slower to 20% slower)
The interesting thing to see is what happens when the resolution increases even more, from 2560x1600 to 5760x1080 (since there is a 50% increase in pixels).