FREE PIZZA, GIRLS and a low 3dmark06 scores with a i5 750 at 4.1Ghz?!

Hi, I recently bought a new mainboard, ram, and cpu, because my old cpu and mainboard fried. The only components that continued to work, were my graphic card hd4850 1gb and my psu. After I install the new hardware, I decided to run 3dmark06 to roughly see what my system's performance would be like. :drool

CPU: i5 750 @ 205FSB x20 = 4.1Ghz
Mainboard: MSI p55 GD85
RAM: 4gb corsair xms3 @ 1640
Graphic cards: hd2900xt 512mb and hd4850 1gb
PSU: Corsair HX620

The graphic card I used for my pc was the hd4850 1gb. The curious thing was that I was getting worse performance than with my previous system (CPU Q6600 @ 3.3 and 4gb DDR2 ram). When I ran 3dmark06 @ 1280x1024 I got a score 13800, which isn't that bad in it's entirety. However, breaking it down I the CPU score was 6500, SM2.0 4900, SM3.0 5700, that is way too low for a HD48501gb. (I used to get 14500 with my Q6600 which scored only in the mid 3000s)
I decided to get a different PSU to see if mine was defected and got similar results with it. I then reinstalled my old 2900xt to see if the HD4850 was defected and got an appalling 10900 :confused, SM2.0 3900, SM3.0 4100, CPU 6300. The difference I did notice with the HD2900xt was, however, that unlike by the hd4850, GTA4 was not choppy. When I used to play GTA4 with the hd4850 I used to get between 40 and 60 fps but it was always extremely choppy.

I don't know what the issue is. All games I try, I either get equivalent or worse performance. I tried stock cpu clock and just got worse results...:confused
Any help would be much appreciated!