Festivums can easily put up with angels. I had two 2" babies that were evil little sods, killed one of my plecs and contributed to the death of another. Also two boesmanni. But.....I rehomed them with someone local, only for one to come back to me not long back. As I didn't want to risk putting it in with my plecs again, it was either euthanise or stick in in the hubbys community (including angels). Must say it's now the perfect citizen, but he can stick up for himself very capably with the angels lol.
He's still only the same size (2") but he's not caused any bother in there, and we have from little tetras to angels in that tank. It's not a permanent arrangement, because I cant stand him lol - it was the hubby who talked me into letting him stay for now. If he remains calm he might go back with the parrots when they get their own tank. But he aint going anywhere near my plecs...