Extremely High GPU Temperatures:

[Soukyuu]

MSI afterburner includes that.. combuster app, was it called? Test your GPU on full load with it, if you land on roughly the same temps then i guess it's normal for your card?

Interesting thing is, I run the game with AO/DoF off, 8xMSAA and both general and drawing distance set to max on a 260GTX (MSI twin frozr) and I'm not having any significant performance drops (40-50fps, 30 in crowded places). Only difference I see is you playing windowed mode and me playing fullscreen. It does make a difference, but it shouldn't be that big.

Even though I kinda doubt it, it could be a hardware defect of some sort, producing higher load on your GPU. You could try running OCCT instead of combuster, it has an error checking mode.

My temps are 60-64°C btw.