I haven't personally seen anyone keep a large male Butt with anything...I have seen smaller specimens in tanks with larger Centrals, but I have never seen them successfully mixed with anything. I think Sauroid is on to something here..we should just call them 'Giant Convicts'.
Fossochromis rostratus is a large Malawi Hap. You really have to see an adult male if full color to really appreciate it. Highly irridescent - rather spectacular looking. I will probably buy another one again, but I am definitely going to wait until my Centrals grow out quite a bit more, if nothing else just to avoid getting 'scarred up' by such a persistent and lively fish.