At least in my display card, the 'optimal' refresh rate is 60hz. This is not what you want.. I set my refresh from 85 to 100hz.
I'm not sure if the optimal setting means best performance, but it sure as hell isn't optimal for the eyes.
If your monitor refresh rate is now 50 when playing aces high and you have vsync enabled, it will limit your maximum fps to 50.
Make sure you run your desktop at 85+ hz and that you run aces high on exactly same settings. Both resolution and color depth.
Changing RAM from pc100 to pc133 won't change anything in your system. You'll still be running your memory and peripherals at 100/66/33Mhz. That means that if you don't overclock your computer, nothing stops you from keeping that old PC100 stick in..
I have 196Mb PC133 and 64Mb PC100 installed in my overclocked 667@901 celeron and it's running with no probs whatsoever.