I'm not sure if this is related to the topic but here is my 2 cents. I recently activated the physics ability of my 8800GT. Sense then I have not noticed any of my games shudder and seem laggy in certain situation. A good example is like in the game GRID... when I slide into the dirt initially when I got the game it would have a brief half second lag while the dirt kicked up. Now it seems much smoother and fluid then this happens. I actually had better control because that half second of lag always made me over steer and spin out. My driving actually improved and thats no joke. Another example, when the Titan blows in BF2142, when the Titans first appears blowing up. I would get that split second of lag right at the first initial explosion. Sense enabling the physics of the card I have not notice that happening. Like I said, it may not have anything to do with the topic at hand but I honestly think that it made a difference.
Just a thought though.... BF2142 is maxed out as far as setting go. I mean MAXED right the hell out using nHancer utility to override the game setting and NV control panel settings. My 8800GT runs it smooth smooth smooth (minus that one little part I mentioned). So if in fact the physics did load onto the GPU I doubt that it made any more of a load on the GPU. On the other hand a game that is DX10 I'm sure would have a much profound and noticeable impact on the GPU ability to keep up.