TF2 looks ubar good (shiny pyros) and so does CoH (with 2x AA I usually get around 35 FPS, would more RAM allow me to increase the AA and get better framerates? Cuz I don't see why the card would be having issues).
Framerates are generally boosted by faster cpu's for processor intensive games, or more powerful videocards with more video memory for video intensive games (or a combination of the two). Having more computer RAM probably won't boost your framerate UNLESS you didn't have enough to begin with and the processor was being impacted by having to constantly swap memory to the hard drive.
Generally a games performance is limited by whatever is the bottleneck. For example, my computer processor is an old 3200+ AMD Athlon with 2GB RAM, but it has a maxed out Invidia 7800 AGP card...I know this sounds old now, but it is one of the fastest video cards I could stick in this computer and is more than sufficient to play Sins...my bottleneck is my processor.
Without really knowing the games in question, it is hard for me to say what is needed to increase your framerate...probably look on a message board related to that game and see what people say works for them. Most games are fine with 2-4GB RAM and are not going to get faster as long as they have the amount they need.