internal graphics sux.. even if you only bought a cheap pci-e (without hypermemory or whatever) you would see a BIG increase in FPS... how many W power sup... do you have anyways?
but its weird, my laptop with Intel GMA900 gets better FPS on full graphics and 1024x768 32bit than you get on low %-6
and remember: Overclocking = more heat = less performance actually.
edit: + integrated graphics uses the processor for rendering etc.. so you're loosing performance on that area too..