which should choose (tank wise) the 55 is 48x12x20 and it has a built in overflow the 90 is 48x18x24 and has an eshopps overflow box both have sumps, skimmer, and return pump. In my current setup i have 2 clowns, one royal gramma, and a watchmen goby pair. I've been in the hobby for nearly two years and really want to upgrade to one of the two tanks so anyone with those tanks i would appreciate any input!