Today I tested my Ver 4 28 Elmarit-M, on a A7.
This lens is a fabulous performer on my M240, but unfortunately is poor on the 24 MP A7.
Based on what I have read on the forum I was pretty sure it wouldn't work on the A7R, but was hoping it would be good on the A7. Unfortunately it was not worth the effort.
The outer areas of the image were very soft, corner light fall off was surprisingly not a problem.
This is without any LCC corrections of course.
I have had zero luck with M lenses on the A7r including the 50 Summilux ASPH, a focal length that in theory should have little problem. Biting sharp and beautiful in center but falls apart badly at the edges at wide apertures. Gets better as stopped down but when I have to stop down to 5.6 and then not look too hard at the edges I start feeling like I'm trying to stuff a (very expensive) round peg into a square hole. My 35 Summicron IV also does some really weird things at wide apertures as well, see: round peg, square hole... I haven't even tried my 28 elmarit after the above experience.
Inexplicably, based on the above experience, my CV 35 1.2 v2 works great on the A7r even all the way wide open with no more aberations than seen on the M9. If it wasn't so darned heavy, I would have given up on the Sony 35 (see last paragraph)
I have a great respect for Leica engineering that they designed sensors that work well with most M lenses but it is becoming clearer to me that if you want to use your Leica M lenses full frame, you need to buy an M or M9 (used M9's can be had for about $4k now, not cheap, but....)
Alas, I did pony up for the Sony 55 and 35. I had to return 2 copies of the 35 before I received one that was right. That was the first time in my life that I had ever returned a lens and I had to do it twice. That has left me a little bit shaken about Sony lenses.