I tried something tonight that had surprising results. My system is antiquated compared to a lot of you.
Duron 850 overclocked to 884MHZ
512 MB pc133 memory Now 768 MB 2 pc133 & 1 pc100
32 MB TNT video card
I had a 256 MB stick of pc100 memory in my parts box. Since I had the room on the MB I decided to install it. After testing all bios setups on the memory I ended up having to reduce the setting from 133 to 100 before everything became stable.
I then went to pcpitstop.com and ran a complete test. To my surprise the rating went up 45 points or 10%. Since I had lowered the bios speed setting, I expected a break even result at best.