Fair enough.
Did the 5D2 work for you? A7rII with Canon 24-70 II or 70-200 II is at least as fast as the 5D2, and more accurate, especially when not using the centre point.
If not (i.e. if you need D810 or 5D3-level AF), then you might need to wait for the A9, or the next generation Sony mirrorless, for AF with third-party lenses to be viable.
I never progressed to the 5D2. My most-used lens at that time was the Sigma 15-30. The Nikkor 14-24 was so much better, I thought it deserved its own body, so I bought the Nikon D700, which seemed tremendous value at the time considering it had approximately the same performance as the much heralded and much more expensive Nikon D3.
For a while I was using two systems, the D700 with 14-24 zoom permanently attached, and the Canon 50D with whatever Canon lens I though appropriate. When the cropped-format D7000 became available, I was so impressed with its wide DR and the potential freedom from all concerns about ETTR, I decided to buy it, together with the Nikkor 24-120/F4 zoom.
I still used my 50D for a while, especially with the Canon 100-400 IS, but when I later bought the upgraded Nikon 80-400 G lens, and a couple of good primes such as the Sigma Art 35/1.4 and Nikkor 85/1.8, and of course the D800E as soon as it became available, the 50D and all my Canon glass became completely redundant.
Having recently dunked my D800E in salt water at the beach, whilst attempting to jump over a stream flowing into the sea, I'm now in the market for a new full-frame body. The A7RII with its potential to work with both Canon and Nikon glass, at first seemed the ideal candidate. However, after reading all these stories about problems with adapters, and the advice from Metabones that Canon lenses designed before 2006 might not work with their adapter, I think that a D81O is a better option for me, considering my circumstances.
Another option is simply to wait a while to see what developments take place. I think I can survive without a full-frame body, for a short time at least.
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