Fair enough. On my system, most games suffer about a 20-40% loss in performance in DX10 mode compared to DX9 mode, but this is likely due to my video card.
It's true that pure 64 bit mode isn't going to help straight computation much. Sure, the extra registers will make some difference, but you won't see it except in some very specific situations.
However, Paolo's original assertion was that 32/64 bit context switches on MacOS X causes overhead. I don't really see how comparing 64 bit and 32 bit Windows to each other has any relevance to that at all.
more than likely is that it isn't a true dx10
game from the ground up. but a dx9 game with dx10 features shoe horned in.