8'x3' footprint, 2' tall for a pair for life would be the minimum I would even consider.
8'x30" footprint, 2' tall for a single male for life would be the minimum I would even consider.
Anything less than that, IMHO is cruel. But as was said above, that 150 will be great to grow them out in for a while. You obviously don't need the larger tank when they're 1" juvies, but when the male gets 2'+, you're obviously going to need to have him in a tank with a width bigger than 2'.