I don't know... the current stumpjumper is awesome. That Zion frame would make a really nice singlespeed setup, or even one with gears. Are you alright with your drivetrain stuff? I think XT equipped bikes cost so much because they have other nice crap on them as well...
Just get like a Sram cassete and derrailuer and such, get the high end ones if you feel like it. Get some FSA V-drive cranks, they probably don't weigh much more than the shimano ones, and you'll have a hard time breaking them.