Finally, done the testing. Sorry for the delay.
Removed the sound card, removed the 1900xtx, tried the 6600GT with 84.37. The stuttering was much much less at 800x600 low settings. In CoH at low settings there were no problems, Prey still stuttered.
Tried the 1900xtx again with CAT 6.9( I think), hardly any stuttering in MW(practically nil). No problems in CoH at low settings but at high settings there were some problems which I will explain later in this post. However now my FPS seem to have taken a big big hit. Earlier I never used to get below 40FPS maybe except 1-5% of the time. Now I mostly started getting in my 30s with occasional glimpses of 40s and rare 50s. Next, I removed these drivers and installed Warcat 6.6, and there was no stuttering with MW again, but I am getting mostly 20s and 30s with occasional 40s. These FPS are really realy bad and make the game unplayable. Removing 4x AA makes a huge help and trying at 10x7 with no AA gets me an average 40FPS compared to the previous 45-50FPS at 12x10 4x AA. Now I feel like I am gaming on a 6800GT/7600GT level card. I wasn't getting lagging in CoH even in High settings except what is explained below. But now CSS stutters.
Another problem I am getting is that I get huge image tearing in my games which seem as if they are stuttering. Another problem is that I feel a weird sort of thing(big and hazy) moving below the ground in my game which also makes the game as if it is stuttering and seems unplayable. This sory of thing I get in CoH demo, Hitman Blood Money(occasional) and Prey. I will post videos of these so that you can get a better view of all this.
I will be trying Gecube drivers, changing RAM slots and trying the SB Live in another slot. Do you want me to do something else? Please help me.