Unless you're gaming includes MMORPGs (eg, WoW) with add-ons and Ventrilo, etc, you really aren't going to see much imporvement going to 8GB.
Unless you are overclocking, you will not see any change in gaming performance going from "value" to "gaming" ram. Faster ram can be an asset in overclocking the cpu. So if you want 8GB, just buy another kit of whatever you have.
Note that some motherboards don't play nicely/easily with ram when all 4 slots are filled . . . you may need to play with BIOS a bit. 2x4GB would ease the likelihood of issues, but the easiest build to get stable is 2x2GB.