Ultimate XC wheelset IMO would be Mavic X3.1 (if going tubeless) laced to some Chris King ISO Disc hubs, using DT or Wheelsmith double butted spokes and aluminum nipples. If you're lightweight and want to go crazy with the cash, upgrade to titanium spokes.
I like aluminum nipples vs. brass because I'd rather pop a few nipples than pull one through my rim.
L8R
__________________
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW, What a Ride!" - unknown
"Your Bike Sucks" - Sky Yaeger