Other than being a slightly better overclocker in some instances the 650i isn not a superior board. The latest tests are showing the 680i with the P30 bios, are performing very closely with the P35s and in many instances even passing them.
AnandTech: NVIDIA 680i SLI: Official 1333MHz FSB CPU Support Arrives
"The NVIDIA 680i chipset has always been a top performer in gaming and this trends continues in our limited test suite. Although the performance differences between the boards are extremely minor, we see the EVGA 680i taking the top score in two of the benchmarks. This is reversal from previous P35 test results that utilized an AMD HD 2900XT card. Still, gaming performance is driven by the GPU, especially in the latest titles, but every extra bit of performance always helps."