I shot the 35 summilux for years and at the time it was made was a superb lens and cutting edge technology. Compared to todays lenses it's only a fair performer. It's soft at 1.4 and good by 2.8 with uncontrolled flare untill you get it to about 2.8. Contrast is loer and flare can destrou your images very quickly. It's particularly bad if point sources of light are in ir mear the edge of the frame at 1.4-2. If th eprice was $400 then it would be a good deal but at the prices they bring , now over $1,000, it's a bad deal. Why pay that much for a lens that's only fair in performance and have to stop it down to 2 or 2.8 to get acceptable results.
Look at the Zeiss Biogon for a stellar performer that tops the new asph summicron. I have both and like the Biogon over the asph summicron. The Biogon is a much smoother tonality than the asph and atleast as sharp if not better with much better flare controll and excellent contrast.
Second choice would be to look at the CV Ultron or PII. Also if the size doesn't bother you and you want the ultimate in speed and flare controll with excellent sharpness look at the 35mm Nokton.
From my understanding there is only one summilux pre asph formula. The difference as to what I haveread is the coatings improved some and a slight tweek to the lens was made. The one I had was supposed to be after that tweek and it still was not a good lens by todays standards.