There are a bazillion (a lot) of factors that go into a benchmark score, such as gaming resolution, game visual settings, game audio settings, overclocking, not overclocking, etc. The list goes on.
Looks like you have a pretty decent level of performance now. What are you trying to do (other than go faster) that you can't do now?
What resolution are you gaming at? And, what driver version are you using for your HD6870?