as far as i can tell, both on paper, and in practice... if you maintain a certain Nr and fly the minimum ROD airspeed as charted in the helicopter's manual, you will arrive at the charted rate of decent. the one difference being that the heavier aircraft will fall faster and gain excessive rotor until the pilot arrests the NR back to 100%. once they reach steady state. both will have essentially the same ROD if airspeed and rotor are the same. if only my VSI gave me more than a 1000 FPM reading, haha.