Check my sig for info
Also the stated overclocks are all rivatuner given ones, currently only riva shows the correct values.
Also to check your overclock for the best possible stability i highly recommend this (
http://www.ozone3d.net/benchmarks/fur/)
Leave it run for approx 30 mins as [Stability Test, 1024x768, Non Fullscreen(unless SLI) and x2 MSAA]
Now the Fur really pushes the card to its limits, so keep an eye on the temps throughout the test.
In theory no game will push the temps this high, its just to guarantee a certain degree of stability and peace of mind