I use a 2 x 8 setup on my XC race bike. Crank is a Middleburn Duo with 29 and 42 rings. I use a LX 580 front mech with the high limit screw all the way in an have it setup for 1st gear on the 29 and 2nd on the 42. Works like a dream and is a great race setup if you don't have massive steep technical climbs where you race, which I don't.
The most popular method to go double for XC race is get an old 5 bolt compact crank (Raceface NEXT LP is the gold standard) and get 29 and 42 rings (or 44 is you have massive top end!) bolted onto it.