I've caught HBCP in my pond up to 16" - I'm sure there may be some larger - I don't fish my pond very often except through the ice - less than 20 times annually.
There is recruitment - I can't definitively state F2 grow slower or are more likely to be preyed upon which is what some literature states. To date, I do not have a population management issue. I wonder if they should truly be used like a triploid - put and take? They have only been present in the main pond fishery for 5 years, certainly not long enough for any solid science to be established. However, so far, they've been a successful addition to my fishery, and have provided several meals and good times on the ice.