3D Mark isn't going to change a whole lot (if at all) in response to system RAM size. The extra RAM won't really help a graphics benchmanrk since even when the video card uses system RAM it doesn't ever have to cache to the HDD. You will probably only notice a performance increase when you have a lot of applications open at the same time, for example, if you were running PhotoShop and DreamWeaver at the same time with a few IE windows open and Winamp playing too. Extra RAM really only helps with speed if your system is caching to the HDD a lot before the upgrade, of course, even if it's not caching the extra "headroom" provided by the RAM upgrade is worthwhile.
Zenmervolt