Hope this formats OK. Data is from cameraquest.com and other sources. Base is baseline of rangefinder in mm. Magnification is effective magnification of viewfinder relative to life size. EBL is effective baseline, or Base x Mag. The last column is effective baseline as a percentage of the effective baseline of the M3.
Camera Base Mag EBL % of M3
Bessa R3A 37 1 37 59%
Bessa T 35.8 1.5 53.7 86%
Bessa R,R2,R2A 37 0.68 25.16 40%
M3 68.5 0.91 62.33 100%
M2 68.5 0.72 49.32 79%
M4 68.5 0.72 49.32 79%
Any mistakes are mine. The order is random. This isn't the only criterium for making a choice, but the info may help when you've chosen other factors that are important to you.
Well, the preview looks like column formatting is lost, but the data are there.