MHz !!!

I have been looking around at overclocking results and noticed that some graphics cards have a lower MHz (mega herz) but it is closer to the core processor. Some people lower the MHz on the processor and graphics cards. So would it be better to get lower MHz RAM too ? I've now got 800 MHz RAM, should i get the lowest i can ?
Thanks a lot !!!!!!!!!!!!!!!!

I dabbled in overclocking the GPU and found no vast improvement and nearly got my fingers burnt as you can literally destroy hardware if you don't really know what you're doing. May be this link will be informative http://www.basichardware.com/overclocking.html .