Performance related problems on a new system

[rane]

Relevant specs:

• Vista x64
  Sapphire Radeon 4870
  MSI P7N SLI Platinum
  Exceleram 2 x 2GB, DDR2 800MHz (4-4-4-12)
  Q8200 @ 2.8GHz

The problem I am having is that some games run exceptionally bad in certain situations.
For instance, Team Fortress 2 goes down to 40fps when lots of players or terrain are visible. What I also found out is that in TF2, I have the same issues regardless of if all video details are low or maxed.

3DMark Vantage: P8981
Accurate system specs: http://kahiseva.ath.cx/systeminfo/systeminfo.xml

Provided this is not expected performance for my system (which I hope it isn't) any ideas what may be causing this?

 

[mpilchfamily]

Its common for FPS to drop some where there is allot of activity on the screen. Besides 40FPS under heavy times like that isn't that bad at all.