Total performance @ high res with the GTX 260 in SLi used as a baseline-
Anyone that's read more than one review knows the HD 4870 wins games like Assassin's Creed, Grid, and Oblivion well. It wins Bioshock in some reviews and can not do AA in that title currently, unlike nVidia cards.
It loses to a stock GTX 260 in: AoC, Crysis, Lost Planet, WiC, CoH, Jericho, Graw2, Gothic 3, PT Boats: Knights of the Sea, Frontlines: Fuel of War, SupCom, and Prey, to name a few. The reviews are mixed.
Anyone can cherry pick a few benches, which I am demonstrating below
, and it's not hard to tell who's a fan of what by what they select.
What's up with GRAW2 performance?
Another thing I noticed is when the GTX 260 loses @ 1920x in GRID and Assassins Creed it's still putting up very playable FPS. The same can not be said for the HD 4870 when it loses @ the same res in Lost Planet-
Another neat thing about the HD 4870 is currently you can cook your breakfast on it.
I'll put my bet on an overclocked GTX 260 winning vs an overclocked HD 4870 in the majority of games. Sure the HD 4870 has a few great wins, and folks seem to be focusing solely on those. Some benches are definitely contested depending on the site you believe.
The bottom line is they are both good buys right now and you wouldn't go wrong having either card in your rig.