I shoot M6 Classic & M6TTL. I prefer the TTL version, only because the speed dial 'goes the right way' as indicated by the LEDS.
Apart from personal work, I shoot assignments using both cameras, ranging from weddings to stage and theatrical work. In the past I used Hasselblads and auto Nikons for the same work. The Leicas rule! ... after I developed a technique of handing, the point of this thread.
I leaned to load quckly, even in near total darness, I work with highest pre-set shutter speed that allows me some margin to vary the aperture according to the light, that best suits the subject. For stage and theatre work, I am frequently restricted to max. aperture, when I only have variable speeds at my disposal. Adrenalin rushes!
Some concert work, eg. orchestras, I need to 'focus' on one instrumentalist, but retain the environment of the orchestra without making the image 'busy'. The Noctiux with f1.0 is brilliant for this, but exposure must be controlled by speed dial. That is why the M6TTL better suits my purpose. An M7 would be a dream because of the auto feature, but the digital M will probably steal my dollars first!
SUMMARY: Every shooting situation demands a different approach to camera technique. You MUST be familiar with you camera ergonomics to adapt without conscious thought as to how you will prioritorize handing. That means practice, practice, practice . . . .