Wouldn't be much- identical codec unless we're talking AVC-Intra. And I don't know of two examples taken on the same stage. Taken from different lighting setups would be meaningless. It's the optics that would help as well. Surely the client gets that a higher quality lens would produce a sharper image and result in an easier key? That said a perfectly usable key can be derived from HVX200 footage shot and lit carefully so I would really push the camera type as the critical point. More a DP with major green screen experience backed up by a good vfx compositor.