Upgraded from D7000 to D600. WOW.

OP mentioned improvement in sharpness etc. Of course the question on lens selection does matter if such is discussed, We do not know if OP is using kit lenses with both systems, or better quality lenses with the new FF system.

That would make a significant difference.

Not saying that the D600 will not improve certain areas, but sharpness is questionable, unless one considers 'perceived' sharpness re contrast / resolution of the FF at same size of APS-C... ot unless better lenese are being used, in which case better lenses WILL make a significant difference.

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.....Just from an amateur......''Sometimes it's to your advantage for people to think you're crazy.”