You should not limit yourself to just the FED2 and the Zorki4. Also consider the Zorki6, a really neat and usable camera.
I have tried all of the main Soviet RF and I have come to find the Zorki 4K my favourite, BUT a lot of that is down to the particular cameras that I ended up with. My FED2 is a bit ratty while my Zorki 4K is really almost unused and works a treat. The "survival factor" is a major issue. Still, the 4K has a lovely bright viewfinder, a wind-on lever and loads of speeds, so it is well worth considering. The most equivalent FED would be the 3, not the 2.
I would agree that the Jupiter 8 is the best of the thread-mount lenses. The Industars are good, just not quite as good as the Jupiter (but agin, that is my experience with the particular lenses I ended up with). A good Jupiter is truly superb, probably just as good as the best to come out of Japan.
My favourite cameras of all are my Zenit 3Ms. I think they are better made than most of the rangefinders and they seem to be more robust too. Despite what I said above about lenses, the Industar 50 on my Zenit is exceedingly sharp. I have another Zenit with a Helios 44, which I have not as yet tested. The SLR lenses have the useful feature that they can focus down to 0.5m.
