I realize that we're getting pretty far off of the original question (relating to image quality), but I would suggest that you keep both cameras. I took a two week trip to Africa and I was swapping my lenses out more often that I preferred. If I could afford to, I'd keep both.
On safari, put that 650D on your 70-200 (to take advantage of the crop factor) and your wildlife photos will have much better reach. In daylight, unless you are trying to track a moving cheetah or something, I think that combo will do great. Put the normal or wide angle lens on the 5DIII and get beautiful scenics, and you can swap the 5DIII onto the telephoto if the distance shortens, the light drops, or the action speeds up. Everywhere else, and for sunrise/sunset/evenings, take the 5DIII. You can hand off the 650D to your travelling companions (so you can be in some pictures) or just have it on hand as a spare.
You didn't really mention lenses or whether you bought these in kits, but you could also pick up a 650D body or a 600D body used or refurbished to do the same thing. Don't sacrifice your whole kit just to have the 5DIII, but if you can have good lenses, a tripod, a flash, and two bodies, I would do it.
Most important, for an 8 week trip, you will need storage space (memory cards, laptop, and/or external hard drive). On my two week trip, I nearly filled all of my cards shooting JPG only. If you shoot RAW or RAW+JPG, you will fill them up very fast. Being gone that long, you will want to keep your files in at least two places. You can do lots of cards backed up to your laptop and not erased, or a few cards backed up to your laptop and an external hard drive before erasing the cards, or, with the 5DIII having dual card slots, you could backup one card to the other and rotate out your backup cards to the bag where you keep your dirty underwear, and nobody will steal them. Cards and hard drives are not too expensive any more, but I would rather haul a lot of SD and CF cards rather than a laptop, ipad, or hard drive.
Post more questions as you prepare. Some of us on here are living vicariously through your travels!