i heard u can use ati tool with nvidia cards as well.
Yea I play around with it on my 7600 GT AGP to learn it before trying it on my main system. Still learning that and RivaTuner.
For GFX tests I just use like a Far Cry or HL2 Demo and loop it. I've also used Lost Planet PC Test to test tangible frame rate benefits.
If something doesn't look right, it's an artifact.