Thanks. Another significant advantage for me is comparative weight. At the moment I'm somewhat temporarily disabled with carpal tunnel syndrome in my right hand. Mirrorless bodies may be smaller than DSLR's but the FF lenses are massive and ATM I simply can't hold them.
For example, the Canon FD vintage 135mm f2.8 here weighs 400gm while the Sigma 135mm weighs 1.33Kg!
a grip or something to extend the camera body down should help you.
on my pentacon i cant remmber the blade count, (i might have the low one) but i do have the god's eye 300mm f4
http://vintage-camera-lenses.com/meyer-optik-gorlitz-300-orestegor-pentacon-300/