I have both, and they are fairly fast growers compared to others. I would think you could get up to two years out of one that size before you had to find a larger home.

The Regal(Hippo) is fairly shy, and might hide in the rock with a lot of unfamiliar traffic in your waiting room. The Sailfin (IMO) is a much more beautiful fish, just not with the striking colors. However, examining a Sailfin closely, the coloration paterns are amazing, and of course the fins are cool.