SpeckleBelly (SBS) as hybrid sunfish of the BG X RES cross can grow to large sizes. This is a link to some naturally produced and well fed specklebelly sunfish from Ohio. There are claims the SBS can grow to 3 lbs.
https://forums.pondboss.com/ubbthreads.php?ubb=showgallery&Number=570913IMO ultimate size and ferilty of the speckle belly IMO does depend on which gender parent was the BGill and which one was the REar. Malone Fish Farm will probably not tell you this information. Some but not all of this information would be available in the Childers hybrid sunfish paper link provided above by ewest.
This From Malone's farm "Populations of Specklebelly Bream™ are 95 to 100% males, readily take fish food, grow to large sizes and are easy to catch."