I'd go with Damienm's suggestion. I understand what you're saying as I have an M6 and a Bessa R4A. I used to have an R3A as well but sold it when I got the M6. I also miss the AE feature on the M6. And the shutter lock!
I have the CV 35/1.4 Nokton lens pretty well permanently mounted on the M6 but if you didn't want a lens this fast then the Color Skopar you mention is also a good one. (I have the 28/3.5 and the 50/2.5). I kept the R4A because I like to use wider angle lenses and often use 25mm or 21mm which the M6 viewfinder frames don't accommodate. If I was going to use a 50mm lens often I'd also suggest the R3A as the viewfinder on that camera is wonderful for that focal length.