i've never used the artifact tester since i run linux, but i would say the best test is to play yur favorite demanding game (ie: ut2003) for a few hours
if it survives that then yur good
but i would be atleast 5 to 10mhz below the point where you get artifacts
so you look alright
also if it gets hotter in the summer you might wanna drop it another few mhz just for safety's sake, hehe