Leica M6 versus Medium Format

[KEN_GERLACH@HP-MountainView-om1.om.hp.com]

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     I am on the verge of purchasing a Leica M6 Rangefinder camera to 
     replace my Pentax 67 system.  I use the heavy Pentax system for B&W 
     photographic art work mainly still life and landscapes and some 
     portraits many times in low light conditions.  I do prefer sharper 
     images but do not require 4x5 system features such as tilt controls 
     and etc.  I usually have prints enlarged to 8x10 or maybe up to 
     approximately 20x30.  In future, I may want to shoot some color Velvia 
     transparency film and print up to 20x30 Ilfachromes or color negative 
     film and print.
     
     Would anyone please answer two questions:
     
     QUESTION 1:
     ----------
     
     What quality results might be expected from final prints (8"x10" and 
     20"x30"), for example in terms of resolution/sharpness, tonality, 
     contrast and etc. taken under two conditions?
     
     Condition A: 
     
     Using a Leica M6 Rangefinder on a tripod with Leica's fast and high 
     quality lens (for example, 35mm, 1.4 f), Kodak TechPan B&W Film 25 ASA 
     or another similar slow and high grain film.
     
     and
     
     Condition B: 
     
     Using a Pentax 67 Medium Format camera on a tripod, mirror locked-up, 
     with a larger 120 negative (2 1/4 x 2 3/4), higher grain TMX 100 ASA 
     Film and Pentax slower lens rated at 105mm, 4 f.
     
     I believe the difference in results will probably be attributed to the 
     following differences in the two approaches:
     
     - lens speed and quality
     - size of negative (e.g.,number of times negatives need to be enlarged 
     for final prints)
     - the difference in film characteristics (grain, tonality, contrast) - 
     the amount of camera vibration (probably more for Pentax 67 shutter 
     assuming even though I still lock-up the mirror when taking a picture)
     
     
     QUESTION 2:
     
     Do you have any hints or advise in using the Leica M6 built-in light 
     meter to determine exposure settings and adjusting for various 
     lighting conditions?  I use a spotmeter with my Pentax 67 very 
     successfully (e.g. using the zone system to predict what zone a 
     specific object in scene will fall) and am concerned about going back 
     and relying on a camera's built-in light meter (average a scene,etc.).
     
     As you can see I would like to use the lighter weight Leica system and 
     still achieve sharp gallery quality B&W prints close to what I get 
     with the Pentax 67 system.  I would be very appreciative if you would 
     offer your thoughts to my questions. 
     
     Best regards,
     
     Ken