I would have thought all sharp lenses will be as sharp on a 5D3 as any other Canon DSLR. :shrug:
I would have thought that the FF sensor is more demanding of lens quality, especially in the corners, and that you cannot just throw any old piece of glass on it.
Very true! Any body had any experience with the Tamron 28-75 on it?

I would have thought that the FF sensor is more demanding of lens quality, especially in the corners, and that you cannot just throw any old piece of glass on it.
A FF sensor is more demanding in the corners, but an aps-c sensor (eg 18mp in 7d etc..) can be more demanding in the centre of the lens - more MP concentrated in a smaller area of the glass so more demanding of resolution within that area.