True, the Tumult does work very well in that sized box. And it does indeed require a good amount of juice in that sized box as well.
The Sadhara driver (12" XBL^2) shouldn't require nearly as much power as the Tumult (15" XBL^2) does in the same 3 cu ft box.
But as John says, if you don't mind the $500 for the Tumult, and can get a big amp to run it (Crown K2 or QSC 3402), and don't mind that it's a 15" driver, and not a 12" driver, go for the Tumult.