Settings Adjustment:
Something I have found and now read about in the ISI forums too, altering some of the graphics setting does not always work until you re-start the game. This could easily lead to quite a bit of confusion for people trying to find an optimal setting.
I would suggest that when playing with settings, you adjust each one in single increments, one at a time and try at least a couple of laps to get a fair idea of the impact on FPS. Also note, that if you turn shadows off or to low, you can get some graphical glitches such as missing body panels.....