I'm not a RAM expert either but I don't think anything you do with 2 sticks vs 4 sticks is going to make any difference. As long as you have enough RAM you should be good. If you're not using all that you have now, then there is no reason to buy more. I have 8GB and don't use it all but when I upgrade to a 6 core or 8 core, i will buy more just to keep my RAM to Core ratio at 2:1 (2GB RAM for every 1 Core of CPU). Other than that, people have done tests with using faster RAM and the results were negligible for video editing and rendering.
~jr
http://www.johnrofrano.com
http://www.vasst.com
