its pretty goood... but u need certain tests to find artifacts a description of what an artifact looks like :
and artifact is anything that should not be rendered and is usually a by product of a bug in the game/drivers or an unstable clock .... it looks like white/black/coloured pixels that appear randomly at the screen, sometimes it appears as a big black or white splash , and sometimes it is a black or white polygon that sperates from a model and jerks around the screen.
If u are overclocking, make sure your video card has some decent cooling, and you DON't have artifacts BEFORE u clock.... its normal to get a few white dots on a handful of cards because of an old bios/drviers.. but anything else means the card needs xtra cooling/is clocked too high...
Heatsink only cards are easy to cool, just strap on a 40mm/60mm fan and it will help the temps alot. Some cards have a built in temperature monitor, this helps with knowing if your card needs more clock or not...
One of the best ways to maintain a stable clock is to LOCK both RAM and GPU frequencies at the same speed, if you have no problems with artifacts but get crash bugs, try this.
Tests recommended : 3dmark2001se + , Halo, Painkiller, Unreal II/tournament , Wolfenstein . in fact, any test that pushes your video card to its limits will do, if u don't have one, use an older game eg. Half Life on max resolution with AA on.