For what it's worth, I've had a couple of Summitars, and a couple of Jupiter-8s and I'm not 100% sure that the Summitars were really much better than the J-8s. I currently have a new old stock J8 [bought unused in the original case] and a good condition coated Summitar, and I suspect you'd be hard pressed to tell the difference except the out of focus areas [bokeh, whatever] are nicer on the J-8 wide-open. The Summitar has pretty wild swirly out of focus areas, whereas the J-8 is smoother, and much less distracting. The former is interesting as an effect, but the J-8 is probably the more consistently useful lens.
The Summitar is a very pretty looking lens, though, compared to the black J-8!
Matt