Stuttering/massive frame rate drop GTX 275 SLI

I bought a new system about two months ago, and its been in and out of repair due to various problems, first starting with a BSOD, failing cards and now a bunch of games stutter, freezing up for half a second occasionally. Games like Crysis, Torchlight and even Titan Quest jump once and a while.

I'm using two stock GTX 275 Superclocked in sli, with the 196.21 drivers. This problem occurs with both one card, and in sli so I don't think it is microstutter

both cards run at around 45 degrees during Crysis

specs are:

Intel Core i7 950 Quad-Core 3.06GHz Retail
Cooler Master V8 CPU Cooler (RR-UV8-XBU1-GP)
OCZ (OCZ3G1600LV6GK) DDR3 PC3-12800 Gold 6GB
EVGA X58 SLI (132-bl-e758-a1)
Western Digital VelociRaptor (WD1500HLFS)
LG CH08LS10 Blu-Ray DVD Combo Drive
Cooler Master HAF 932 Full Tower ATX Case
EVGA GeForce GTX 275 Superclocked X2 in sli
Thermaltake Toughpower VGA Power Express 650W (running both video cards)
Microsoft Windows 7 Pro 64-Bit (OEM)
Mushkin (550150) XP-650AP 650W ATX Enhanced

This problem occurs in many games, even older ones
Any ideas on how to fix this?