I am new to the sport of mountain biking and was wondering if forum readers could shed some light on the appropriate set of hydraulic brakes for my given application.  I recently bought my first mountain bike and it came with a pair of stock Avid BB5 mechanical disc brakes (with 160mm rotors).  The brakes are insufficient when my rides involve steep downhill descents and, as a result of this, I lack the confidence needed to negotiate critical situations. I am now in need of a braking system that can remedy this situation and one that will accommodate my 6'4" 250 pound physique.