I had u43, have NEX and M9. Jono said almost all I would say.
Problem with u43 and NEX is... wide angle. Simply 35mm 1.4 acts as 50mm (and f/2 in terms of DOF on NEX). There is also chromatic aberration, that does not exist on M9.
Attaching it to u43 gives 70mm (and f/2.8 in terms of DOF).
Wider fast M lenses cause often problems on crop sensors at edges area (soft, red corners, etc).
Whate else?
The same lens at NEX vs M9 - much more details from 2nd. The higher ISO the bigger difference. In all tests NEX controls noise better. I also see that after opening RAW in LR. But in reality - when I develop RAWs - I have better results from M9, more details (of course after downsizing).
Additionally you can shoot with longer shutter speed with M and focus faster, especially against NEX who misses EVF (but only in center of the frame, what can be important with fast lens from close distance).
I think one day - FF EVIL will appear. Without customized microlenses - it should give you a lot of what M9 gives - for focals 50mm and longer.
Many people see magic in photographs taken at f/0.95 or f/1.4. As you see - you won't get that magic at cropped sensor, as you won't get that DOF.
Problem with u43 and NEX is... wide angle. Simply 35mm 1.4 acts as 50mm (and f/2 in terms of DOF on NEX). There is also chromatic aberration, that does not exist on M9.
Attaching it to u43 gives 70mm (and f/2.8 in terms of DOF).
Wider fast M lenses cause often problems on crop sensors at edges area (soft, red corners, etc).
Whate else?
The same lens at NEX vs M9 - much more details from 2nd. The higher ISO the bigger difference. In all tests NEX controls noise better. I also see that after opening RAW in LR. But in reality - when I develop RAWs - I have better results from M9, more details (of course after downsizing).
Additionally you can shoot with longer shutter speed with M and focus faster, especially against NEX who misses EVF (but only in center of the frame, what can be important with fast lens from close distance).
I think one day - FF EVIL will appear. Without customized microlenses - it should give you a lot of what M9 gives - for focals 50mm and longer.
Many people see magic in photographs taken at f/0.95 or f/1.4. As you see - you won't get that magic at cropped sensor, as you won't get that DOF.