are there any recent benchmarks for these to cards on things like crysis as the only ones i can find are older and because the 4870x2 is new the drivers were weaker and so now the performance is probably better.
Are you going to SLI the GTX260? Otherwise the HD4870X2 is going to totally dominate a single GTX260 in any game supporting CF and will be about equal in all others.
The 4870x2 is certainly much more expensive than a gtx 260. It is also far more powerful. Neither are particularly new. The 4870x2 is substantial overkill at 1680x1050.