is it the AGA stand? i have a 65g and i used a standard 15 gallon tank and had lowes cut some glass panes to my dimension...Use a little acrylic and wallah, a sump w/ baffles for not alot of cash.
Wes is right on point, a 15 gallon AGA sump leaves you room for a 5.5 gallon tank next to it to use as an Auto Top Off reservoir. Plus a 15 gallon tank leaves you room to work. If you go with a 20 high you'll find yourself unable to get to anything on the bottom.
Will a 15gal tank give me enough room to have seperate chambers to fit my return pump and a skimmer and pump? This is a concern for me. Right now I'm using a Pro Clear Aquatics 125 wet/dry. and both pumps are in the same area, and it's sooooooooooo tight to fit anything else in there. Also I have no idea where to silicone the baffles and how it should be set up. And yes I have an AGA tank and stand, and would LOVE to fit a 5 gal tank next to the sump for an ATO.