Cool little set up Mark, but as you stated you'll need to upgrade tank size eventually. I like the rock work, you have a knack for natural looking decor.
As for the O.B. Peacock typically being more aggressive, that is due to the genetics of the O.B. Zebra which was hybridized with an Aulonocara species to create this man made fish. Of course there are exceptions with aggressiveness, or lack thereof such as you're observing, but be watchful in case your O.B.s start to get an attitude as they grow.