It is not the machine, it is the graphic card which handles 100% of the environmental mapping. Takes a bunch of video RAM and video card bandwidth to do this in real time.
The problem is, if you crank up AA and max the shadow sizes, along with full environmental mapping, you can max out 4GB of video RAM pretty quickly, in which case, it is not going to matter how fast the video card is.
Oh, SLI performance sucks, in Aces High, due to the poor SLI profile NVidia supplies for the game.