There will probably be a pretty big speed up when the drivers improve. And the price point advantage could be pretty big ... in a few months a pair of HD4850s may cost around $300 and outrun a GTX 260. And that same comparison may hold true of the HD4870 vs GTX 280.

Another thing is, from the size of the chips, I'm guessing AMD can make a 4870X2 but Nvidia can't make a 280X2. If that's right, a 4870X2 probably *will* be the top card for this generation.