Upload & Sell: On
I think this an interesting subject for discussion and I will speak about my own personal experience. I was an early adopter of the 5D and 5D II (pre-ordered those cameras before they came out) and I was not disappointed - although the AF points (outside of the center AF point) leaves much to be desired. But the files from these cameras are very good. The 5D III is a significantly more efficient camera I've heard, and the 24-70L II is even better than prime-lens quality. According to Roger Cicala's tests, it beats all other Canon primes in terms of resolution including the T-SE lens.
Having said that, I think the OM-D can do almost anything that my old 5D II could do ... and in some areas much more, such AF speed and accuracy, and dynamic range. And with good lenses, such as the Olympus 9-18, 12/2, 45/1.8, 60/2.8, 75/1.8 ... the Panasonic 25/1.4, 45/2.8, 7-14, etc ... it can compete with some of the best Canon L lenses.
I have not had any buyer's remorse, nor do I miss my 5D II and L-lenses. Not at all. The files from the OM-D are simply amazing - at least as good as what I was used to with the 5D/5D II. Don't get too hung up by the small sensor size, as that is very deceiving and it doesn't tell you half the story.
So I would not hesitate to leave the 5D III behind and take only the OM-D with a few good primes, plus a good zoom like the 9-18 or 7-14. Forget about the 12-50 kit lens if you want the highest quality files that you could get out of the OM-D. The OM-D + kit lens will not be able to match the IQ you can get with the 5D III ... but a good prime or zoom certainly can ... IMHO.
I am trying to decide on taking my OM-D on a 1 month vacation trip versus my 5D3. As a result I have been reading up on the OM-D and this thread has just incredible photos. While I am still researching I thought I would add a few from the past year.