I have just finalized some floating point performance test of the GeForce GTX580. As expected it was the fastest single precision performance I have ever measured. The peak single precision performance was 849 GFlops, and peak double precision performance was 193 GFlops. For comparison the Tesla C2050 delivered 550 GFlops single precision peak performance, and 250 GFlops in double precision performance.
I hope the results may be useful. I will soon upload it to Torben's Corner - but it will likely have to wait for my Christmas holidays.