I would of thought an FPS increase would largely depend on the graphics card you've chosen. I doubt the extra RAM would do much and SLI/XFire isn't natively supported on the Mac side...
Try downloading the Demo, that will give you a good indication of whether this game is for you.
As for me I managed to play Crysis on my Mac Pro at around 20 fps. Doesn't sound good but that was with everything set on high, sometimes I had to shift into medium near the end of the game but it was all good.
The specs for my Pro are as followed:
Quad 2.66GHz Xeon
2GB Ram
GeForce 8800GT 512MB
I'm sure you would be able to best that with the buffed up specs. 😎
I would of thought an FPS increase would largely depend on the graphics card you've chosen. I doubt the extra RAM would do much and SLI/XFire isn't natively supported on the Mac side...
Why would you mention the mac side if the game isnt supported on OS X?
Crossfire is fully supported via windows, and SLI is only supported on the 7300GT video cards, which arent even an option for crysis.
The most FPS one will be able to get with crysis is with two ATI Radeon HD3870s which are compatible with both mac and windows and then crossfiring them in windows, which would give pretty decent results at 1680x1050 resolution.