I just upgraded from a 50 gal to 120 gal and everyone seems to be getting along okay. I used to have a convict pair that ruled the tank and had babies constantly (one WHOLE batch even survived), but I had an accident in my tank while I was gone and lost the female and all the babies I hadn't managed to find homes for. I think I'll leave my male a bachelor, he's much less aggressive (even though I loved my convicts, great colour and lots of personality).
I'm really thrilled with my new tank.