Gary E, I use my 75f2 Summicron on one of my R3's (a R3M) as it gives me free standing 75 frames. No stupid 50/75 combo as in my M's! I have used the 75f1.4 with it too and though a bit tricky at f1.4 and 1-1.5 meters, it works well (better than the M's as a matter of fact).
The 40f1.4 SC/MC is a perfect fit for the R3 series. It is a bit tighter than the 35, but not enough to create problems. It is also a very good lens, sharp, nice contrast and useful at f1.4. The choice between SC and MC is not critical. The difference, particularly in black/white is very subtle. Mainly a bit more detail in deep shadows. The SC can flare, but you really have to work at it though. I haven't shot the MC and SC side by side in the same light so I cant say if the SC flares easier than the MC. I tend to use them without really looking at which is which.
The R3's really spoils you for viewfinders though. Once you used one, the M's look a bit "dinky" by comparison. The only finder better than the R3 is the Zeiss ZM one - and you can almost buy two R3's for that money!