AMC,
It's your pond and if you want cats, go for it! They should pretty much keep the BG in check. In fact, the State of Texas recommends a CC/BG combo for your size pond.
If you want to try something different...and have a fish that's great eating, won't overpopulate, and is a great sport fish, you might consider HSB. I haven't tried them in that size pond, but if you also feed them, I'd expect them to do just fine...but again if you want cats, then by all means, get them.
