having them around the same size is your best bet, I always keep mine at the same size b/c even though one might dominate, but it makes it harder to try to eat the other one and etc if they are around the same size. I also keep cichlids together that shouldnt be but agression evens out when they have their own territory and cant fit in to one anothers mouths..
Anyways yes a 55gal should be fine!
Also if you have that you have more options for other fish and peacocks are very colorfull fish when you find the right ones!
Anyways yes a 55gal should be fine!
