For two GTX460's in SLI you wouldn't notice much difference in games even if you OC higher. They are powerful enough to play anything already, so I don't see how you would need more power, except for benchmarks perhaps.
It would be benificial to press the GPU clock speed higher though, the VRAM is quite high as is. Also remember to tweak the voltage for the core to keep it stable.
The biggest problem on these cards is the VRAM suffering from stability issues under OC'ing. The VRAM is the "limiting factor" much more than the GPU, so feel free to press the GPU a bit more and refrain from pressing the VRAM much further, you could seriously damage your card. It heats up badly. I tried pressing mine's VRAM a little and it went berserk with the temps, so I dropped the VRAM speed and upped the GPU speed a little until I got a good, stable OC. Temps dropped, stability increased and I got much better FPS in games and a quite impressive increase in 3D Mark 2006 score.
Hope this helped a little.