Did you have like 6 tabs open and you clicked on the wrong forum to post this? This question has been beaten to death here
http://photography-on-the.net/forum/
This is a car forum...
In my opinion the 5d Mark II or any 5d is a toy compared to the 1d. Given my statement I have a 1ds-mark III. Full frames are great for taking landscape pictures. If you want to make huge prints I would go with a full frame but a crop camera would be sufficient
IF YOU WERE TAKING PICTURES OF JUST CARS.
EDIT: Saw this in the picture sharing section and posted b4 it was moved.