I agree with Ralph. My 80mm is no sharper than my 50mm lenses, but for mechanical vignetting reasons I am forced to use a 63mm for 35mm negs.
Ctein tests (I recall) show that the shorter focal lengths are often sharper and that as long as you do not have coverage issues, soft corners should not be an issue. Certainly hasn't been for me. That 63mm is killer sharp and so is the 50mm Neonon I have.