If I was going to africa for 8 weeks, a once in a lifetime trip for me, build quality would be a major consideration....depending on how I was traveling, I would be very tempted to have two camera bodies just in case one failed. But this would have me leaning to a 7D at a minimum or keeping the 5DIII between the two options you give.
Regarding image quality under good lighting conditions, there is a very small difference, but it may not be discernable unless you are pixel peeping. Even then, it is tough. This is a comparison of both camera bodies with the same lens under the same conditions. The differences are there, but I can understand why you don't see a difference when printing on your printer: http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=458&Camera=792&Sample=0&FLI=0&API=3&LensComp=458&CameraComp=808&SampleComp=0&FLIComp=0&APIComp=3
Honestly, I was surprised by how comparable those two images were (BTW, if not familiar, you toggle back in forth between images by moving the cursor onto the image and off the image).
I don't know where you are going on your trip, but I think you should consider that in making this selection for two reasons: light and weather sealing. If you will always have good light, then there may not be much of an IQ difference. However, in the rain forests of Costa Rica, I needed ISO 6400. Amazingly little light makes it past canopies of rain forests/jungles. You will want the 5DIII or 6D if you need to shoot at greater than ISO 1600, definitely ISO 6400. If you will be in tough environmental situations, I can see wanting the weather sealing of a 7D or 5DIII.
So, build quality/ISO performance would be two critical factors to me in your decision making. The other would be reach. The 650 being a cropped sensor (same with 7D) will have 1.6x more reach. So, if you have a 200 mm lens, it will behave as a 320 mm lens would on the 5DIII. Of course, on the wide end, you would need a 15 mm lens to give you the same field of view as a 24 mm lens would on the 5DIII.
Once in a lifetime trip to Africa, money a slight factor (no big white lenses), I am probably taking a 5dIII, 24-105 f/4, 7D, 100-400 L and something like a 50 f/1.4 or 35 f/1.4 for low light options. If I didn't already own the 100-400L, I would consider the 70-300L or maybe the 70-200 f/2.8 II with 1.4x and 2x extenders. Carry those around in a good backpack or something like a Storm 2500 pelican case. Also, I'd have a CPL, and some graduated ND filters.