jpsdad, I think the mouth gape has to figure into it. A BG has to key in on much smaller food sources than a LMB of the same age because of gape. I believe that's why HBG grow faster for the first few years - a larger gape than regular BG can utilize more food sources.
Probably key to a benefit of a larger gape would be the availability (supply) of the larger organisms. I have fished some trophy BG ponds where I never caught a LMB > than 12". The typical BG might have weighed as much as the typical LMB. Given the age of the ponds, it may well have been that the largest LMB I caught were 10 years or older. So at least in that case, gape wasn't the determining factor for which fish grew the fastest unless perhaps it was the reverse. This smaller gape of the BG and their focus on smaller prey might possibly have given them an advantage to grow to larger weights than the LMB. This is not to say that there are not circumstances where larger gape is an advantage to growth ... its just that it is not always the case. The stunted LMB - Huge BG pond is a contrary example.
Genetics seem to limit the growth in the length of fish and when they are able to consume more than required for this growth ... they can get really fat. But the growth, possibly driven genetically through hormones, is subdued in BG relative to LMB. They are wired to grow slower and have lower specific consumption (weight prey per weight predator per annum).
I failed to but meant to also mention that if male Florida bass in Florida were to tend beds more than 1 per annum ... that might explain in part why the males are so limited in size relative to the northern males.
