If inbreeding is going to yield fish like those, I’ll take it. All kidding aside, within a species genetic control of growth rates is usually masked by environmental conditions. Food (quantity and quality) is the most important factor affecting the growth of fish, assuming water temps are suitable. In the case of limestoners groundwater sources at 51-52 deg F extend growing seasons in comparison to freestoners. Additionally, forage biomass is typically greater in limestoners, at least those that have not been substantially degraded by various sources of pollution.
Furthermore, Hammer is a blended system with at least one limestone and multiple freestone ST populations that can freely mix, so it is not as though these populations are genetically isolated.