Performance unaffected by graphic settings (~20-30 FPS) Options

[DuggeDank]

Hi there,

This is more of a question than an actual problem, but anyway, I'm not seeing much change in my game when I alter my graphics settings. Currently I'm running most settings on high except for postprocessing (and visibility 3000) and I'm getting an FPS of ~20 in both forests, cities and open fields. When I turn everything down to absolute minimum I'm only seeing a slight improvement, maybe up to ~30 FPS. If I turn everything up to absolute max the FPS drops to ~10. The FPS is also slightly higher on Utes than on Chernaurus.
I'm running FRAPS to check the FPS.

Is this normal? I was expecting a much higher increase when things like visibility and AA where turned down.
The game isn't unplayable at all, I'm just a little curious about this. I do feel like I should be able to get a little better performance out of the game.

Here's my computer specifications:
Motherboard: ASUS M4N72-E
Processor: AMD Phenom2 X4 940 3.0Ghz, AM2+ Black Edition
RAM: Corsair 4GB (2x2048MB) 1066MHz
Graphics card: GeForce GTX 260
Windows 7 RC