You don't want to hear this, but why do you want to stick with fullframe?

I've gone back from a Canon 5DII to a Fuji X-T1 based system. Fuji's IQ is on par if not better than the Canon. If you're going into towns, there's the fantastic 27/2.8 pancake and the 18/2.0R, making your camera pretty light and inconspicuous looking. As a bonus, shooting JPEG with the little Fuji is very well possible. Where, with Canon, I used to shoot RAW all the time (and thus needed to PP everything), this is almost never necessary anymore with the Fuji.

It's not without its limitations of course, but so is the step to Sony. There's loads of glass available for the Fuji, not so many for the Sony. I wouldn't hesitate!