You pose a great question OP. The fact is, its pretty easy to get caught up in this latest tech game ... and honestly, there is a bit of 'all the cool kids have ____ so therefore I need to get a ____ to be cool' in photography...
I am amazed that so many posters here are trying to recommend to the OP to keep the 5D3 which is so much more expensive and way in excess of his needs. Too many users in this forum are gear heads. The gentleman stated that he couldn't tell the difference with his test shots. He knows enough about photography to understand the impact of lighting and lenses on the results. And I am sure he understand the differences with features etc. His main concern was IQ! Yet he was expecting something different - its a real eyeopener if you ask me. We assume that everyone has the desire to pixel peep and find the most discernible difference while forgetting that photography is an art and a pastime not something to keep our wallets empty. I say to the OP to SEND BACK THE 5D3 and stick with what works for a little money and go from there. Later down the road if you want the performance or 61 focus points etc you could buy the 5DMk4 or something better. In the end i think this guy knows something that us gearheads dont!
Another excellent post.
Now my two cents worth. The gulf between film and digital is immense. Even the most inexpensive digital cameras will give far greater image quality than what most of us long time film shooters ever saw with film. The differences between the two larger digital formats (APS-C and "full frame") is much smaller and really only apparent at the margins (shooting high ISO or extremely large prints, for example)
If you shoot at ISO 400 or below, you can easily print as large as A1 with no discernible loss of image quality using an APS-C camera.
I am going to suggest a third option for you: Consider the 7D, if you like the handling of the 5DIII but are satisfied with the APS-C image quality. Both use the same sensor, but the differences are in the build quality, handling, autofocus and frame rates. The 7D is relatively inexpensive right now, in anticipation that a replacement model will be announced in the coming year. But, it remains, in my opinion, the best crop-frame camera available.
Why the 7D? Because I assume that a trip to South Africa will involve some wildlife shooting and under those conditions the autofocus and higher frame rate will help you get shots that you might not otherwise get.
In addition, I would suggest that if you return the 5DIII you look seriously at a longer telephoto lens. Again, assuming you are planning to shoot some wildlife, I think you will find the 70-200 zoom a little too short even on an APS-C body. The obvious options are the 70-300 "L" and the 100-400 "L" zooms.
The 70-300 "L" is newer, a little lighter, maybe a tiny bit sharper, easier to carry in a camera bag and the autofocus is a bit more responsive. The 100-400 "L" gets you an extra 100 mm, which is no small consideration in shooting wildlife and remains a great lens at a reasonable price.
Finally, I'd suggest you take a little time to learn RAW processing. I see no reason to shoot RAW + jpg, unless you need to immediately upload or print your images from the field. Even if you shoot in RAW and do nothing more than open the files and save it in Photoshop as a jpg, you will still have the RAW files later to work with.
Going from a film camera to a digital camera is amazing, but be prepared for something even amazing-er when going from processing and printing film-based images to processing and printing digital images using RAW. It simply offers options that could never be achieved with film – adjusting the color temperature of the image, tweaking the exposure over an almost infinite number of gradations, adjusting whites, shadows, blacks, contrast, highlights, etc. all independently. Creating smart objects that allow you to tweak one part of the image in one way, another part in a completely different way and a third, fourth, fifth, sixth part if you choose and then merge the various pieces in Photoshop. All with the ability to return to your original exposure at any time if the need arises.