Here are a couple of resources for you.
Erwin Puts on required base length & rangefinder accuracy:
www.imx.nl/photosite/leica/technics/rfaccuracy.html
Depth of Field calculator:
www.dofmaster.com/dofjs.html
There are numerous depth of field calculators available on line. The link above is just one. If you're not comfortable with that one, do a search & try another. It's useful to see just what you're dealing with. With a 50/1.4 mm lens wide open at 3 feet, your depth of field is one inch - not much of a margin for error.
There are different issues involved in what is a desirable base length. The first is your own eyes & how well they see. Second is the
minimum that is required. Third is what is desirable for ease of focusing, which is a different matter. Fourth is the size of the prints you desire. Fifth, is how well adjusted your rangefinder mechanism is at any given time. If the rangefinder is slightly off, this will have twice the impact on the R2 or R3 than it will have on a Leica M because the base line is half the length. This is true regardless of magnification because it has to do with physical length as opposed to your ability to see & discern the image(s) (magnification).
Of course longer base line is not an issue in most photos - depending what you shoot. Focal length, aperture, & subject distance all factor in. You may not need the increased base length often, but it's there when you need it.
