They are beautiful! My favorite of the sunfishes. Almost all of the sunfishes get that big, and some even bigger. There are some dwarves, tho. Great candidate if you want something different in the pond, tho!
I'd be worried about the aggression. Sunfish, like cichlids, can get aggressive. Plus. Pumpkinseeds live in my backyard (well that is also where my pond is, but they live in the river behind my house). If I want them, I just go fishing! They are a game fish in my area.