A 35 is a 35 is a 35 in terms of field of view and DOF. Some are more fiddly than others... and honestly, pre-focusing and letting your DOF carry you would be the ONLY way to shoot the Fed and the J-12 in the street.
And you're right... I've had a number of Zorki 4k and Fed 5 bodies over the years just to play with, and I've never actually been able to bring myself to try to use them for anything serious. They'll take photos... but they're not well finished nor a pleasure to hold or use. I'd even go so far as to ask you not to judge rangefinder cameras as a genre by the Fed you have any more than I'd ask you to judge autos in general after driving a Yugo.
Regarding the SLR-RF body choice though, it really boils down to how you're comfortable shooting.