I've tested v2 and v4. Both yield color vignetting and blur in the far corners until you stop down to a middle aperture. V2 might be a little better than v4, or that could have been sample variation (after all these years of use) or user/tester error.
40 Cron turned out to be the shortest focal length that you can count on to cover the frame well – clearly better than 35. (And Leica WATE and MATE both work well at all FL bcz they're retrofocus designs.)
With Kolari mod you can open up 1 or 1.5 stops farther. Sorry no examples bcz I now have the Kolari mod.