Scombs are the slowest growers and ultimately the smallest.
The tat I had was pretty slow growing as well. It grew maybe .5" a month.
My armatus has grown from 4.5 to about 6" in three weeks! FAST growers.
Ive never had scombs, but from what Ive read tankmates need to be peacful as they are a skittish fish and can be nervous around boistrous tankmates. My tat could take just about anything. I would suggest you throw one in with a Dovii, but my tat took, as well, as dished agression pretty good.
I havnt had the armatus long, but so far he seems to be more territorial then the tat. For example, my tat would chase away a fish that was bothering him first. The armatus will chase away any fish that gets in his territory regardless if the fish is acting agressive towards him.
Long and rambling but I hope that helps...