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Currently hard to find any published meaningful results on 400 series SLI v 5800 CF, the Guru3D ones are a tad inconsistant and the hardwarecanucks while not bad results wise isn't using the best or latest of drivers.
Very interesting, seems to move them more towards ATI's idea of smaller dies at higher frequencies.
Take the following with a pinch of salt, of course we dont what the final specs will be:
So 256 cores at 900mhz compared to 480 cores at 700mhz so very roughly the GF104 has ~69% the performance of GTX480.
So GTX490 (2xGF104), given a 70% sli scaling factor, would be ~117% the performance of a GTX480.
Techpowerup reports the 5970 is 128% the performance of a GTX480@1920x1200 so I suppose GTX490 wont be faster than the 5970
GTX470 in SLI does beat the 5850 in CF in many if not all cases