I agree about the Summicron 50/2.0. I have owned the "latest" 2.0 for about as long as it has been available. It is a great lens at a "reasonable" price. You might well be able to find a very good "used" ex&le at a significant discount. As an aside, I am lucky to have the new M50/1.4 as well. The M2.0 and the M1.4 lenses have a very different ability to "paint an image". With NPH 400 I find the 1.4 to be somewhat sharper ( but not unpleasant ), and with a wonderfully accurate ability to separate out various colors in a very pleasant way. Better then the Summicon? No, simply different. The difference is not simply one of the extra "stop". Although I am still learning, for portraits of my wife I might well use the old and trusty 50/2.0 ( or the 75/1.4, but not the 90/2.0 Asph, and perhaps not the 75/2.0 if I owned one! ). For landscapes in Patagonia I used the 50/1.4 to wonderful effect. I think several of the "newer" designed M and R lenses ( the R 1.4, and now the new M 75.2.0 ) may well share a similarity in the images produced. Indeed, the glass used and the design (s) appear(s) to be very much the same. I cannot speak to the quality of the images on slide film, nor on black and white film. Although not completely germane to your question about the Summicron 2.0, perhaps another members can help us with further observations. To conclude: Have no worries about the M 50/2.0. The lens will serve you very well for many, many years to come. Try to read Erwin's reviews of the various M lenses. Although he has some technical details, many of his comments about the various lenses are interesting and demand no expertise in the reading of MTF graphs and the like. Best of luck, and let us know how you make out. One other caveat: Be aware that many of the well intentioned and sincere comments you will read about lenses are personal opinions, and there are very few absolute "rights and wrongs". Indeed, I have heard of increasing numbers of Leica photographers returning to some of the earlier 50mm lenses because they enjoy the quality of the images produced. Furthermore, we have all seen images produced with those older screw mounted 50mm lenses, and I for one would have been very proud to have created some of those images.
Sorry to be verbose.