OK, so I bought an ATI HD4850 1Gb card and(of course) started to OC it. It went like this(core clock/memory clock, stock is 665/950, tested the stability for 15 minutes every step in cs:s): 680/950, 700/950, 720/960, 750/960 -- glitch, lowered it to 748/960 worked fine then 749/960...