Keine Ahnung ob es schon verlinkt wurde, aber zum Thema M-Objektive und Sony A7r tönt es bei Luminous Landscapes (Michael Reichmann) recht positiv:
"For some photographers (myself included) putting Leica M mount lenses on the Sony A7R may be reason enough to break out a bottle of Veuve Cliquot champagne and celebrate. Using an M to E adapter (I have a Metabones), virtually every Leica M lenses that I own works well on the A7R. Some of the ultra-wide and very wides do vignette, so be aware of this."
http://www.luminous-landscape.com/reviews/cameras/sony_a7r_hands_on.shtml
"For some photographers (myself included) putting Leica M mount lenses on the Sony A7R may be reason enough to break out a bottle of Veuve Cliquot champagne and celebrate. Using an M to E adapter (I have a Metabones), virtually every Leica M lenses that I own works well on the A7R. Some of the ultra-wide and very wides do vignette, so be aware of this."
http://www.luminous-landscape.com/reviews/cameras/sony_a7r_hands_on.shtml