One thing I have considered is the PSU. It's a generic 90W AC adaptor that gets reallllly hot after a while.. Could this reduce the available wattage leading to a slower CPU?
And before you ask again, the temps stated are the maximal temps.
PS: If this could help
I have an M4300 precision that has a D830 motherboard. Pci-e1.1?
I have reduced the textures used ingame to the 3% version of the original mones. They are now smaller than the 128MB of the GPU...
I have set my nvidia config to the maximal performance possible, no vsync, no AA or post effects, 1 prerendered frame, optimised trilinear, everything!