A few lines to add to your quandary :
1. As you are probably aware, Leica bodies older than the M4P don't have a 75mm frame (no new lens in the 73/75mm range between 1931 and 1980!) - so you'll have to guess using the 50mm lines.
2. Anyhow the 75mm frame, when present, is bordering on the unusable. Even the official Leica website is quite candid about it:
So you'll be guessing anyhow.
3. The Ms' combined view+range-finder is not only easier and faster to use, it is also in practice more accurate than a separate rangefinder (such as that on the Bessa T, regardless of EBL), when you look for a split line at the edge
of the RF window:
4. Same with real TTL metering - faster and more accurate than a separate meter, and smaller and lighter too (incident metering is another story altogether). That, and 28+135mm framelines, was what lead me to add a M6 to my M2. There are lots of M6 around right now...
5. I concur that the Summilux 75 is a demanding, but highly satisfying lens. Mine (1st version with separate hood) focuses very smoothly, contrary to what I expected.
6. My personal hit rate surges when I have either enough time to mount the magnifier on my M6/M2, or enough light to reduce the aperture to f/2 or smaller.
7. You'll probably end up selling the Bessa after you have used a Leica M for a significant amount of time. Bessas are well-designed and well-built cameras but when you have tasted the 'real thing' you develop a taste for luxury. Well, at least *I* did.
By all means keep us posted!