The lakes I referenced are fertile - they're all fertilized, the 150-acre one by TWRA and the 56-acre one by moi (previously by a man who works for the owner). Added fertility is just more plankton for the GSH and shad to hog from the bluegill.
Here's what I think: bluegill may get pretty good-sized in extremely optimal, unusual circumstances such as the phosphate pits in FL that Eric mentions, but they'll never reach their maximum potential in BOW that have significant numbers (and the numbers will be significant if they're introduced) of either GSH, threadfin, or gizzard. I've wondered for a while now why the FL state record for bluegill (2lbs. 15 oz.) is smaller than the records of several states farther north with drastically shorter growing seasons; but if these other forage species are very common in FL, that could certainly explain it. Most state-record bluegill came from ponds, including the world record (Ketona Lake, AL, 1950, caught by T.S. Hudson on a topwater bass plug); ponds, until recently, usually didn't have GSH or shad. Just my opinion on the matter.
As to controlling gizzard shad, hybrids don't get large enough to eat an 18" gizzard shad - nothing short of a striper or a muskie or a flathead catfish is going to eat a really big gizzard. And even with one of those species it would have to be a really exceptional fish that doesn't come along every day.
On catfish, I agree with you 100% - if you plan on feeding bluegill, skip the CC unless you enjoy frustration and wasted money. In my observation they don't just outcompete the bluegill, the bigger CC will bully them away from the food so they get little to none. A ten-pound CC tail-slapping a 9" bluegill is akin to a normal-sized pondmeister such as myself trying to block Albert Haynesworth - ain't gonna be pretty.
