Thanks for the responses.

I have little interest in any super fast lenses. 50mm f2 is probably the most demanding lens I'll use, maybe a 50mm f1.4/f1.5 in the future, but I don't foresee a 50mm f1.0 in my life time.

I didn't know much about the rarity of the 0.58 finders but the prices of M6's, M7's, and MP's make the external viewfinder more attractive .