First of all, let me say that I wish I could back my opinions up with some sample pics, but unfortunately, the vast vast majority of my pictures are yet to be scanned.
I found the 4th version summicron and the 40/rokkor very similar interms of sharpness, bokeh, general feel. I love the 40mm FOV so that was another factor in keeping that one over the summicron. Quite frankly, when i bought my first 4th version I foolishly expected it to "change my life" because it was so hyped up on reviews on the internet. king of bokeh blah blah blah...
Well, I was "underwhelmed" with the summicron - it was good, but basically like the M-rokkor. So I sold it and bought another one in case I got a bummer example. It was the same as the first one, good, but didn't blow me away. Then the 8-element came along. Even after my first roll with it I could see a difference - the resolution in the center was incredible. The slight fall off in sharpness towards the edges when wide open contributes to the nice out-of-focus effect and make the subject snap out more, if that makes sense. My only other f/stop is 8 (a basically shoot at f/2, 2.8 or 8), and here the lens is just a nice, all-round, sharp, not too contrasty, pleasing 35mm wide angle. I love the 8-element.
by the way, all these lenses are basically the same size, i.e., nice and small. The 8-element has an infinity lock, which I'm not crazy about, but can live with. Ergonomically, I find the rokkor best for me, by a slight margin. I prefer black lenses (as YOU know), but the chrome 8-element still is a keeper.
My dream is to one day own a chrome M2 or M4 just for this lens.