I would like to put a large tank in my basement, where I have lots of room and a concrete floor. I currently have a couple of 55 gallon tanks, so what I'm looking to do is get a tank that will allow me to keep larger fish than is possible in a 55 gallon. (As opposed to a larger quantity of the same fish). I want larger and different fish (right now my largest fish are Rainbows) I see most 90 gallons are still only 4 feet in length, but wider and higher than the 55 gallon tanks. Does this allow for larger fish, for example, some of the fish that reach up to 12" in length? Or is a 6 foot tank required for most of these fish? Locally there seems to be a huge jump in price between the 90 4ft tanks and the 100+ Gallon 6ft tanks. Thanks for the help.