OK, now for the third time: There is a significant speed advantage. That's why one lens costs more than the other.
This whole thread was started based on the premise that 1.5 versus 2.0 doesn't really matter because it's "only half a stop" and why pay for that?
For pointing out that this is simply wrong, I'm now being vilified.
Indisputable. Also, in the real world, there are differences between nominal and actual apertures, and between f/stops and T/stops, to say nothing of how flare can 'fill' the shadows and make a lens seem faster than it is. On top of all this, 1/6 stop (the approximate difference between f/1.4 and f/1.5) is unlikely to be perceptible.
From my own experience, and that of my friends, the chances of finding a good Jupiter-3 are a good deal slenderer than the chances of finding a good Jupiter-8, partly because there are so many more Jupiter-8s around and partly, as rxmd pointed out, because people tend to hang on to the good ones and sell the bad ones.
As someone who bought his first Zorkii-4 maybe 40 years ago, I find it quite amusing how cameras and lenses that were regarded at that time as pretty indifferent (and which were a lot newer and usually in much better condition at the time) are now praised extravagantly.
Finally, anyone who thinks that a Soviet copy of a pre-war Sonnar (optimized for contrast in the days before lenses were coated) can compare in resolution with a Summicron (coated from the start, optimized for resolution) has presumably never tested good samples of either against one another.
Cheers,
R.