From memory, in still air, they both glide the same distance...the heavier one gets there quicker...that's if they are both gliding at their respective CLmax.
If you're talking both doing 300kts the heavier will travel further....probably because it's closer to it's CLmax than the lighter one....certainly in the real world you tend to need to start your descent earlier when heavy than when light...because we descend to a fairly fixed speed schedule....M.8/290/250kts or similar...rather than at CLmax.