Not much. The impact of a 45% protein level would likely be greatest at the fry to tosai stage.... before the fish is ever sold to a hobbyist. Many years ago, the much missed Ray Abell imported a feed especially produced by the Niigata breeders coop for feeding fry and tosai. It was 48% protein. Ray stopped importing it because the extra high protein added expense without benefit for the nisai and older koi he kept and sold. He instead imported a formula that was around 38% protein.
I think the bigger difference between JPD and Saki-Hikari is the probiotic used by Hikari.