Rick,
I'd like to offer a couple of comments. First, if you want to raise some sizable HBG, you need to have some predators in the pond. Even though HBG are 80 to 90% male, they will still overpopulate a pond, slower maybe than regular BG, but they will overpopulate and leave you with many, many small fish.
It is not recommended to mix regular BG and HBG. If HBG is your target species, then you want to minimize the Fx offspring and keep the hybrid vigor in the target fish. Adding BG to the mix will cause reproduction to increase substantially and lead to less desirable crosses.
As related to outbreeding depression, I don't question that it ocurrs, but do believe that overpopulation and stunting is many times over a much larger concern. I think some folks mistakenly identify inbreeding as a cause of fish stunting when in fact the main cause is fish overpopulation. Not scientific, but I've been raising an Fx in a small micro pond and its growth is outstanding and comparable to the F1 parents.
You have a wide choice of predators for your situation. LMB, HSB, maybe rainbows. HSB offer a good choice for small HBG control and great fishing. They can be completely controlled in numbers because they do not reproduce.
I noticed your close proximity to the Lake. Is is possible that over the existance of the pond's lifetime, water (and fish) from the Lake could have encroached on your pond?
p.s. in my own case with HBG, I'm running a 5 to 1 ratio of HBG to predators(HSB) and thus far seems to be working
