Originally Posted by timcook

The extra energy stored by a big person does not give them a higher velocity over a small person. That extra energy results in them achieving the same velocity (in a vacuum), since they are heavier they need more energy to achieve that velocity.

Assuming all potential energy is converted to kinetic energy (oversimplified), then PE = KE so m*g*h = 1/2*m*(velocity)^2. So you have mass on both sides of the equation, they cancel, and the velocity is then independent of the mass of the rider.

That said, if you remove all those simplifications (vacuum, 100% conversion efficiency), the final velocities won't be the same... but it has absolutely nothing to do with the extra potential energy being stored. The equations become more complex, as detailed by some posters above.