Top system build,But I get chopiness and lag!!

Rainbow six vegas,splinter cell double agent,battlefield 2,dark messiah,half life 2 and pretty much all the games I play I have a little chopinesss and lagg.The wierd part is my fps never drops I always have stable fps and yet it's still choppy and can stutter.Can anyone spare a minute to tell me what would cause this bad performence? I have the latest directx,nvidia 97.72 drivers and sound card drivers.I have the latest p24 evga Bios update.

System specs are....

EVGA 8800gtx
Thermaltake armor
EVGA 680i moterboard
core2duo E6600(2.4ghz STOCK)
2x1gb of corsairs 6400C4(4-4-4-12 at 2.1V)
Silverstone zeus 850watt
WDraptor 10krpm 150GB
Sound blaster XFI xtrememusic

 

Single player or multiplayer?

 

stutter=memory problem (usually), possibly/probably a bad mem stick. try each stick by itself, isolate the bad stick.

nice build, im jealous