I've been facing the same problem since 4 days already and I still haven't figure out it yet. I'm getting 5200 3dmark05, low HL2 and DOOM3 (lower than x800xl and 7600gt) results (3dmark06 from some kind of reason will not finish benchmark) but F.E.A.R. @ 1280x920 with everything set at max give normal result (avarage 40 fps - i think it's not bad).
I have installed the newest drivers for everything, new OS win2k.
What the hell can it be?
-P4 2.8 @ 3.6
-2x1GB OCZ GOLD
-P5WD2 ASUS
-OCZ 520W, 28A on single 12v rail
-Sapphire X1800XT 256MB