An AX850 is based off the Seasonic X850 which has been rated to safely and reliably pull over 1000watts in tests by jonnyguru and others. It's basically an overspec'd 950w unit.. The X750/AX75 has been rated to pull over 900watts safely and reliably as well and is ofcourse overspec'd.
As you can tell. These units are severely overspec'd for their ratings. Hell.. these are units are based on one of the most efficient, reliable, and highest quality power supply line ever designed for the consumer market.
Asking if they "will have enough" power is quite insulting tbh lol.
Yes they will have enough power for crossfire / sli and possibly tri crossfire / 3 way sli.
As jsc stated. Why the 12gb ram? You're running dual channel with a BD which does best in a 4x2gb or 4x4gb config. Unless you're doing 3x4gb config or a 2x4gb+ 2x2gb config; that's really an awkward amount of memory to get.