Here is what I did and recommend to try... Before I made the switch I wanted a test run so I picked up a used Sony A7 for 800 bucks. Barely used, shuttercount was 3500... Then I picked up a cheap manual EF-NEX adapter (25ish from Fotodiox). So for 825 I was able to test the system with my EF lenses, although wide open only, no aperture setting. If I hated it I was able to sell it in 5 minutes for 750... the fact is I don't, I absolutely love it. I shoot the sony more than I did the canons simply because I can take it everywhere and it is not a hassle. I came from a 1Ds and a 1Ds II combo which I got tired carrying around... [IMAGE'S LINK: https://flic.kr/p/rgPUbA]Sony A7 Canon 135L
Since then I picked up a Canon Fd 55 1.2 non aspherical for $220, an Olympus Zuiko MC 28 f/2 for $190 and my favorite the Konica 40 f/1.8 for 60 bucks.
I'm in love with the EVF. This thing is insane. You can literally see the DOF and the bokeh in the electrical viewfinder (my old cameras did not even have live view). I set the camera to Auto ISO (limit to 3200 or 6400), I manually adjust shutterspeed (depending on focal length and subject) and I set the aperture on the lens picking the DOF I want. I can see how it changes by turning the aperture ring on the lens (the viewfinder brightness stays constant to a point as the camera increases the ISO for me). There is a dedicated exposure compensation dial on it so I can adjust "brightness" to my liking. When I push the shutter button the live view I'm looking at freezes and that is my picture (with a little bit of lag of course). DONE. I was blown away when I first learned this...
For the battery life concern: the 1Ds and 1Ds II shared the same battery at 325g. The 1Ds II was able to do 800-1200 shots on a freshly (!) charged battery but I always had to take at least one extra just in case. So that is 325g extra weight. The Sony A7 aftermarket Wasabi battery ($20 a pair charger included) is 42g so I can take 5 of it and still be ahead of the Canon monster weight-wise.
All that being said I had a hard time tweaking the colors to my liking. I think I found a good setting which gives me colors I like but I miss the Canon colors. My Canon bodies are so old that I'm keeping them just in case.
This was taken with the 135L wide open manual focus (the full size version is also available on flickr for pixel peeping):
, on Flickr
This is for gearheads, I took pictures of the camera with all the lenses I own:https://www.flickr.com ...4/sets/72157650643320611/
Seriously... 800 bucks for a year or so old full-frame camera... how cool is that???