Well the obvious choice is the 460 SLI since it scales to the 480 GTX which is a better card than the 5870. I don't think you'll max out on either formats though, you'll probably be able to play pretty well though. 460 SLI's just scale well, also you won't find heat issues there. But if you plan to upgrade further than if you got a 5870 now, later if the crossfired it would be a beast setup. Since the 480GTX has heat issues and things like that. You could also try the 5850, i personally have one i think it is fantastic. But that'd run you about 560-600$ to crossfire, while the 460's will run you bout 400$-430$.
2 460's will run circles around a single 5870. just listen to other people's warnings about heat, the top card can get pretty hot if your case isn't well ventilated. also, going 460's in SLI means you have nowhere to go if you want to upgrade unless you ditch both cards entirely.
benefits now = 460 SLI is king
future benefits = 5850/70
both are great choices though, cant go wrong with either setup IMO
The 460s are the better deal IF you don't care about heat, noise and power consumption. Otherwise go with the HD 58**. If you're trying to decide between the 5850 and 5870, get the 5870, as xfire don't scale as well as SLI does.
SLI 460's would WAX the 5870, they even destroy a GTX 480. The only reason I would choose something else is if I was planning on getting dual high-end cards. Power consumption is something to think about, but it isn't outrageous or anything.
As far as people's claims saying that you need to monitor temps... you should NOT even be worried with the heat SLI 460's produce. They are very cool cards, even with 2 of them you will still be running cooler than a 5870, so that's hogwash.
dude please don't refer to crossfire as Xfire, Xfire is a program, and you sent me for a loop.... lol... =D.
I just wanted to add I can run on a 5770 bad company 2 maxed out accept for AA and AS (at 4x) and in DX11 mode, so a 5870 should be fully maxed, and same with the 460's... I haven't done much research into them... though (mostly I look at ATI's stuff.... yeah I am cardist??[is that the term?]) The temps would rise from the fact they are extremely close, and limits airflow
If you are going core i7 get the coolermaster elite 310 case, great airflow....