In Prouty's book he says that a heavy helicopter will come down slower in autorotation. That seems contradictory... from the fact that a low disc loading is better. I assume he means that a particular helicopter will auto better at a higher weight because the parasite drag and power to the tail rotor is fixed. Therefor if more potential energy is available at altitude then the descent rate can be reduced. Still a bit confused.
A glider can increase its speed with added water ballast but the descent rate is not improved, actually increases the sink rate. (I think)
The Hiller Hornet could not be certified because of the high autorotation sink rate (about 3500fpm) and the reason was thought to be due to drag from the tip ram jets. The tremendous noise didn't help the design much either.