As I'm in the process of acquiring a 5D2, I planned to fit the grid screen, which is what I currently use with my 5D. Information says this is optimised for f5.6. My lenses are f4 or f2.5, although may get Zeiss 21/2.8 and EF 85/1.8 some time in future. Are there any disadvantages to this screen vis a vis standard fit on the 5D2.