Well.... weight does not actually affect your speed. Aerodynamics play a larger part in it and so does the drafting factor. If you pass him from behind you are in some way benifiting from the draft. The only way weight helps you is through momentum, that is, it will take more force to decelerate you than a rider who is lighter, but that soon runs out and then the reverse holds true on the accent. If you remember all objects fall at 9.8 m/s ^2, no matter their mass. Perpendicular vectors do not affect each other so the pitch of the road in no way determines your actual speed, it's gravity you are trying to overcome which....is parallel to the movement (up or down) you are trying to acheive on the hill.