Cartridge impedance loading question

I load everything at 47k these days as I now use an Atma-Sphere MP-3. I have tried different loading for my MC cartridges but hear no difference. I remember talking to Keith Herron several years ago at a RMAF show. I asked why his phonostgae did not have loading options. He pretty much gave the same answer as Ralph. Ironically though the next version of his phonostage did come with load options, but While he never admitted as much to me I think he did that for marketing reasons.