Originally Posted by
Vessbot
Let's say, each aircraft is doing its own best trying to descend as steeply as possible?
Well then the limitation becomes the Vmo. Assuming Vmo is a fixed number independent of mass, both aircraft descend at the same IAS, the heavier one should have a higher L/D ratio (more lift for the same amount of drag) and therefore a shallower descent angle (more track miles).