Peter--
Is yours a Jupiter 3 (50mm f:1.5) or a Jupiter 8 (50mm f:2.0)?
The Jupiter 3, 8, and 9 are all direct copies of Zeiss Sonnar prewar designs, but coated. So they share the Sonnar characteristics. You might look at some of the threads where 50mm and 85mm lenses (also 35mm for the Jupiter 12) are compared. The Russian lenses perform quite well.
Bottom line about these lenses is that they are tremendous value for the money. BUT you should assume--don't even imagine otherwise--that any Russian lens in Leica mount MUST be adjusted to work on your Leica. This can cost maybe $25 to $75, depending on the amount of cleaning and lubing and shimming. It is well spent. There is some debate whether Russian Leica copies actually used a different rangefinder standard or, on the other hand, were simply assembled to wide tolerances. After some careful work, they seem to take great pictures.