Don't worry about it. It's most likely that the programs such as Geekbench or Xbench are not testing the full potential of the RAMs, such as how many apps can run at the same time, etc. Scores do not always represent the quality nor the real world. If you would like to run the test, do what I did:
While on 2GB RAM, I ran 30 application and see how well it performed (glitchy, laggy, freezing, etc.)
Upgrade to 8GB RAM, run the same 30 applications and see how it goes (smooth, no lag, no freeze. Even SC2, Safari, and iTunes can run at the same time, which is amazing to me.)