GPU stress test tool?

I OCed an 8800GTX to 612/1500 stock memory. I use the latest Nvidia driver, ATItool 2.6 doesn't seem to like my setup, and I see two yellow dots there constantly even though the program never reports any errors. Those two yellow dots are there even at stock clocks. I have read that ATItool is not compatible with many newer Nvidia cards and the newer Nvidia drivers. This includes the Geforce 8 generation.

I ran furmark at 1280*1024 at 4xMSAA for 30minutes and it was fine, but furmark doesn't report any glitches like ATItool does. But I have read that if there is any error the program should freeze. Is that true? Also, I'm not sure how accurate the temp sensor on furmark is, because it shows GPU temps at 10C higher than ATItool and Everest.

And is there some other stress tester for Nvidia GPUs out there that reports errors like ATItool does?