3ft wide by 8ft long is plenty. They do get huge but the odds of growing one to over 30" in a home aquarium are slim at best. 96x36x24 would be just fine so long as you dont have too many other large fish in there with it. In my opinion the ideal realistic tank for adult cichla and LMB in the home would be 120x48x30. More would be grand but most people dont have room for tanks much larger than that, even in a large house. You could always go taller and get more gallons but it really isnt necessary unless you like wet arm pits or dirty substrate.