Far be it for me to contradict Jim's excellent testing – so I'm not going to !
But there is a 'but' ..
I use (and own) the Zony 55, both the Cron and Lux 50's and a Sigma 50 Art ( F-mount). - all used on a Sony A7II. Extreme corners are a problem on the Leica lenses and I would only use the Zony 55 and the Sigma for stitching purposes. But the 'Lux has 'something' about it, particularly for portraiture and crops that I just can't let go.
Prior to the Otus, it was generally considered 'the' lens, one of Leica's best ever. I think it still is and, yes, I do prefer it to the clinical examples of the Otus, that I've seen – but that is a totally unscientific, personal (and probably biased) POV.
In comparing these lenses on the Sony Ax series, one thing to bear in mind is that the Sony has a particularly thick sensor stack- hard to measure but Roger Cicala ( who keeps
a database on sensor stacks) has estimated it at > 2.5mm. Removing the stack,
in his words 'the most noticeable difference was in the outer 1/3 of the image area. The modified and unmodified cameras were just about identical in the inner 1/3 of the image with the greatest difference in the corners.'How different is the rendering and if you could choose one for the A7 which one would it be?
It's probably my least used lens but also the one I'm least likely to let go of ..
Incidentally, if you can find a 75mm Lux (the pre-ASPH version) I'd also grab it , if financially possible, allegedly Mandler's favourite and with good reason.
Perhaps try the 'Lux on the A7 before committing ?
