I need to compare your dxdiag outputs side by side, which I will endeavour to do tomorrow for you.
nVidia control panel settings.
This is your next area to concentrate on, it's late. The whisky has been good. Again I'll defer any further comment until tomorrow.
Save to say your comment on a slide show running a particular co-op mission on TS earlier suggests, to me at least, that you may benefit from tweaking your Anisotropic and Anti Aliasing settings.
I found that even with a 3700+ cpu, a 7800GTX GPU and 2Gb RAM that I got a slide show under certain circumstances.
nVidia control panel has outstripped the capabilities of IL2, and will endeavour to offer more than IL2 can cope with.
This results in smoke and explosions bringing your system down to it's knees.
I will note and post the specific settings for you tomorrow.