This is for SL and R shooters primarily but may be of interest to others as well.
I shoot with an SL. I own the ZM 35 f1.4 Distagon. It is exceptionally sharp, clean and well corrected. I also own a Summicron-R 35 f2 (v2). The rendering difference between these two lenses is fairly dramatic. The ZM is what I would characterize as clinical, while the R is organic with more subtle tonal transitions. As a result, when I want a 35mm lens, I usually grab the Summicron-R, which is certainly plenty sharp in its own right. At f4-5.6, the corners look just fine. That's good enough for my purposes, as I have learned not to obsess about corner sharpness at wide apertures. Of course, the f2 maximum aperture costs me a stop of light, but so far it has not cost me any photos that absolutely required f1.4.