Mixed food sizes lets all sizes of fish feed. That is why GFC is made in all sizes. All sizes works fine. 600 is bigger than 500. My feeders don't throw that much in 1 second. None of the directional pond feeders I have seen (Aqua Pro , Sweeney and TH ) throw that much in 1 second. Pellet size should be 20% of the fish's gape. BG from 4-5 inches up can easily eat 600. Under 4 inches can eat 500 better.