I don't know if I may need to fine tune my D7100, but the 50D seems to be sharper for me than the 50G, but my old AIs 50 is sharper than both of them!
You have realised what a lot of reviewers have claimed. If you search the net there are at least three reviews of 50mm lenses starting from F1.2 to F2.8. They make an interesting reading.