There are indeed some attractive choices! I have lenses in 35mm format and medium format with this ~75 degree angle of view, but with f/4 and f/3.5 apertures. So for me any additional lens had to feature more speed, or there was little point. I've been doing environmental shots, mostly in office/shop interiors, and the f/4 apertures have required 800-speed film. That's ok in medium format, but the smaller negatives call for slower films and in turn that means faster lenses!
So, f/2.8 is probably fine... The Leica Elmarit is very compact, and that's good. The Biogon ZM is also very compact, and the choice between these two is likely one of preferring the "look" of one over the other. For another stop in speed, the Ultron gets awfully large, but is economical. I figured I'd probably be happy with it, but there's just no doubt the primo choice is the Summicron, amazingly no larger than the Elmarit. I just decided the speed and size were both important and went First Class for no regrets. I do also have the Biogon-G f/2.8, and while it's for a different camera system, it'll be interesting to see the differences.
For an RD-1, it's a different ball game, as far as I've heard. Lenses can take on different characters with digital sensors than they do with film. Maybe better to avoid high contrast lenses, and I hear the Ultron is a real winner with the RD-1. Someone just recently posted a sample or two shot with the Biogon on the Epson...
Samples: First a shot of a gent with the Biogon-G at about f/2.8
Second a shot of a lady with the new Summicron at around f/4
Third is a mystery shot of a young lady with neither... your guess?