I agree with BlueAncientOne and will include the Rocky in his description. For lack of a better term, the 'Canadian Geometry' (short sloping top tube) can be twitchy, yet are great for tight singletrack. For open course xc racing you will be less stretched out, thus perhaps slower, however if your courses include tight technical singletrack you can make up for it. Ride them all and see which one you like best. If you're shallow (like me!) the Rocky has, by far, the nicest paint job!
Oh yeah, I love my short sloping top tube Rocky, it's very sweet to ride. Also, the Easton aluminum frame doesn't beat me up like some say aluminum does. Compared to my aluminum Norco beater, my Rocky rides like a cloud.