I get screen lag sometimes and I didn't think a 4870 should struggle with settings on 1280x1024, medium settings, AA=1, AF=2, v sync off, HBAO off? Driver is 10.5 I believe, one of the recent ones. Just some more info, processor is a q9400 stock, 6gb of ddr2 ram, vista 64. Is the 4870 512mb running out of memory or something else?