That's said, i was fiddling the graphic settings today and found my fps almost doubled

(from about 15-17 to 30-35) in windowed mode when switched from full screen mode at same resolution and settings(1920x1080, max settings,no AA). It's a pleasant surprise, of course, but i don't understand, do the two modes(windowed vs full screen) make the GPU work differently somehow?
Anyway, gonna play the game in windowed mode from now on
