Honestly, the best size for one is a 120 (48"x24"x25"), because you get a good amount of width, and height, which this fish needs (mostly width, for turning). A 40 gallon breeder will actually get you by for a good while, because of it's 18" width, but you either need to plan on finding a new home down the road, or upgrading. The standard 40 gallon isn't very generous in width (I think it's 13" or so), so your fish won't be able to turn very comfortably when he starts hitting the double digits. 18" is about the minimum width you'd want.
If anyone has anything to add or subtract, please do. I am by no means an "expert".