It's a bigger jump from a 1.6 crop than the 1.3 I had. The ISO is good enough on the 5D3 that pushing it a stop to compensate for the 1.4 that I used a lot was no big deal. I have A3+ prints at ISO 2000 that are superb.
I have a mk1 7 d which I shall keep as Im happy with ,range of L glass 600f2.8. 300 f2.8 etc for wildlife, but think the IQ could be better? Should I go 7d mk2 or 5d mk3 . I enjoy macro ,wildlife and landscape.