I am going to S. Africa for a safari. I have my 5D MkII but I will also carry my friend's 50D for 2 reasons:
(i) as a backup if my 5D MkII suddenly has some serious problem, which can then ruin my holiday, and
(ii) to avoid changing lenses in the dusty wild jungle while in 4x4 drive.

Am seeking advice from the veterans here on the following 2 alternatives during the safari itself:

use the 100-400 with the 5D2 and 24-105 with the 50D
Pross: Full Frame will give better colors at 21 MP with low noise at sunrise & sunset when animals are active due to 5D2's better noise control.
Con: 24mm on crop-frame 50D will become almost be 40mm making me lose some real wide angle shots.

use the 24-105 with the 5D2 and 100-400 with the 50D
Pros: 50D will give 140-640mm effective range and I can get 24mm wide angle shots on the full frame 5D2
Con: Noise could be an issue for the 50D at sunrise & sunset when animals are active and wildlife shots will be at 15MP vs 21MP on 5D

It's a bit tough to take a call between these two, so inputs from some of the experienced guys might help me. Thanks in advance.