50mm is quite long on the rd1(s) - 75mm equiv FoV. i have used quite a few 50's on my rd1 before i permanently loaned it to a good friend in the UK. i have had all three lenses and still have both of the noktons. i have not, however, had an opportunity to try the 1.1 on the rd1 body, so i can't comment on whether it blocks the viewfinder/rangefinder. i am guessing it will slightly.
because the nokton 1.1 is *very* sharp and the transition from in focus to OOF is very smooth, a lot of people find its rendering somewhat clinical/sterile. in other words it seems to lack any discernible character (such as Noctilux, Summilux, Canon .95 or 1.2, or even the jupiter 8, etc.) which many find a bit of a put off. it still has a razor thin DOF on a full frame body. if you were to get it, i would *highly* recommend a 1.33 magnifier to compensate for the short effective base length.
the heliar has a nice character even with the rd1's crop factor. it's also a nice compact comfortable lens - just don't forget to open it... i actually miss this lens quite a bit. OOF areas render beautifully. it has nice contrast without being too much so (like nokton 40mm). it's great for both film and digital.
the nokton 1.5 is a bit 'bulky' compared to the heliar or other smaller 50's. it's OOF rendering is nice, however avoid a bunch of straight lines in the background, such as branches. it gets a bit 'swirly' when they're in the OOF area.
i highly recommend you first decide if 50 is the right focal length for you. i used 35mm far more than 50 on the rd1s body, and 50mm is my favourite rangefinder FL... my choice of the three listed would be the Heliar. i haven't tried the new version, but it looks like it is the same as the slightly older classic / 250 yea like i had. or you might also look look at the zeiss planar, which is a fantastic lens on this body. good luck and happy hunting! you'll probably end up with a few 50mm lenses anyway...
edit - i should probably point out - i do have the 1.1 on my m8 as my walk around lens and alternate between it and the nokton 35 1.2.