There is probably not enough difference to bother changing bodies.
I used my 1D MK III and 5D MK II in my studio interchangably.
One thing to consider is the long battery life of the 1 series cameras if you use liveview, and I always use live view in my studio, the 5D MK II battery will expire long before the 1D MK III, so you will need to spend $200 for a AC adapter.
My 1D MK III included a AC adapter, but I usually did not bother, since the battery would last for 2 hours of liveview use and a lot more.