4870x2 should be *slightly* faster than two 4870s in CF, and blow away the 4850. It also has a decent chance of not suffering from micro stuttering because of how it is designed. (Uses shared memory instead of a bridge according to reports.) It will be a long time though before many games run at low enough FPS on 4870s in CF for the stuttering to be noticeable. Unless of course you are running at like 1900xsomething.