what does the other one eat? it may not be so much that the one eats massivore, but what the other one is eating that may be holding it back. at the same time, they don't look terribly different in terms of condition from this photo, so it may be that one just has the genetics for slightly larger growth.
impressive specimens reGARdless--
--solomon
PS-- FYI i have nothing against massivore...i add it to the regular feedings of shrimp, tilapia, and smelt that i feed to my gars.