performance problems with a home built system

Hello everyone,

I assembled my system like 3 weeks ago and since then I have noticed that I don't really get the same results as done on various benchmarks, actually it's not 10-20% but in some cases it's over twice less, like in games

My system:

Core 2 Duo E6700,
Asus p5w dh deluxe
corsair xms26400 cas4 2x1024ram
Gigabyte GeForce 7600gt,
2xWD1600JS in RAID 0
1X WD2500KS
Zalman 9500
other stuff I don't think is important, but if needed, will mention later, when I get back, a little bit in a hurry right now.

Ok, so, the thing is, while playing games I noticed that I don't get any near the fps I see in various reviews andw ith weaker systems but same graphics card. Quake 4 is terrible at High, 1280x1024, 8xaniso, 4xaa, average fps is like 23-27, drops to 10fps quite often and rarelly goes above 40... battlefield 2 plays smoothly just still, fps below what I see others get... same with all the games. Synthetic benchmarks don't show that anything is wrong though. Also the actual performance in various programs doesn't seem to be what it should be :|

Would apreciate any help
Will be back in 7 hours