Technical descending is all about rider skill, confidence and willingness to take risk. The best descending bike is the one that you feel most confident on. Buying either bike isn't going to turn a poor descender into a downhill rocket.
Maybe I'll get blasted here, but while I'm at it; buying a $2000 wheelset isn't going to turn a cat5 racer into a pro, a 12lb bike isn't going to make you climb like Contador if you're an old fat guy, and aP4 isn't going to make a guy with tweety bird legs as fast as Zabriske in a TT. If you're worried about a few grams on the bike, go for a ride instead of eating that slice of pie. If you want to descend better, practice, practice, practice.