Maybe i should've rephrased my question better...With the H5/H6's digital sensors, does it make sense to use an HMI back with bodies newer than H4?
H4 and newer, will give you True Focus, film doesn't care what the body is, but it will love the lenses.
The film doesn't care, but the body won't fire if the back isn't compatible and as far as I know only the H4X is compatible in the H4 series.