How can I know if the speed of RAM is the bottleneck rather than CPU speed?

I have a lot of RAM, 20GB to be precise. However they are not exactly high-end RAMs.Two of them are Kingston 8GB RAMs with 800MHz speed and the other two are some no name brand 2GB RAMs with just 600MHz.

I am having performance problems, even just when using multiple demanding programs. I have slightly overclocked the CPU but that only helped slightly, and only for some things.

I started to suspect that the CPU is fast enough for my needs, but it spends too much time waiting for information to come from the RAM. I am not entirely sure how this is internally handled, but I know that my friends with similar CPUs are not having these problems when running the same games.

So my question is, is there a way to determine that the RAM speed is a bottleneck in the speed of the system? I cannot afford to upgrade my entire system, but I can afford faster RAMs if that would help.