In actuality an aircraft will glide at constant dynamic pressure. If we assume that all glides are performed at the best L/D and that the aerodynamice are linear, then all glides will have the same best L/D angle of attack and occur at the same best L/D lift coeffieient. This is independent of the weight. The flightpath is also invariant with weight and is given by the L/D ratio. An increased weight at the same lift coefficient and flight path angle will require a proportional increase in dynamic pressure to support it. Therefore an increase in weight should produce a faster speed down the same glideslope.