I'd recommend you look at bootcamp or perhaps VMWare's fusion. I bootcamped my Macbook Pro and the response under windows 7 is impressive. You have to give up some disk space, but I now keep photos on a small portable USB drive.
What I'd like rather than more pixels in the 5DIII is greater dynamic range and less noise at higher ISO. I have friends who shoot Nikon and have less noise than the Canon. I'd also like to have a better AF like the Nikon has. Donning my fireproof suit now! LOL
Less noise... -> less noise at the per pixel level, try scaling up or scaling down and then compared images.
On that note, if you can, I'm sure you could cook up a nice comparison as you have access to the cameras.
You could always use the still life scene from Imaging Resource, normalized for the same resolution. Pay particular attention to the black velvet cloth and black cup in the lower right, the shadows behind the bottles and the detail and color in the threads along the upper right. On my 23", 1680x1050 monitor, a horizontal image viewed at 40% is roughly the same size as a 12"x16" print.
You know, a link would help
You can download the raw images if you start from the camera review. At ISO12,800+, images need a LOT of noise reduction.
Thanks for the link