7870? Maxed out.
Unless you play in DX11 (you actually have to download the patch for that).
With DX11, maybe a step down from maxed.
I have a 6970 crossfire, and Crysis 2 fully modded - that's with DX11 patch, High-Res patch, MaLDo texture pack, Blackfire's mod - kicks my system's butt.
http://www.youtube.com/watch?v=CmupVG1uPoU&list=UUZXSZdGb3Su8RvR5QuRyeqw&index=2&feature=plcp