Znalazłem coś takiego. I chyba tym się nieco pokieruję.

The 40mm f/2.8 is sharper across the frame @ f/2.8 than either the 50mm f/1.4 or 50mm f/1.8, but as soon as either of them are stopped down to f/4, they're substantially sharper than the 40mm f/2.8. (Note: the 50's reach peak sharpness right around f/4 and dont add much by going to f/5.6, especially on crop bodies.)
Still, I think its safe to start recommending the 40mm f/2.8 instead of the nifty fifty as a starter fast prime ... at least once the street price settles.