Its funny but I have no idea for mountain biking - now ask me about road and I could tell you. I think when Im mountain biking Im more interested in getting through a ride without falling off. If I manage that and I ride stuff I walked before Im happy. I must admit I love downhills on the mountain bike and I try to go as fast as my fear factor will let me.
The most effective way to do it, is to do it.
Amelia Earhart
2005 Trek 5000 road/Avocet 02 40W
2006 Colnago C50 road/SSM Atola
2005 SC Juliana SL mtb/WTB Laser V