Having been instructing twin engine helo's for years as well as flying them, the auto's I've practiced have shown that a/c wt not surprisingly has a major effect on rotor speed in auto as well as that developed during the flare. But the environmental conditions have as great an effect. 19,000lbs on a hot and high day makes for a rapid arrival flaring 250 - 300' but add 25 kts wind and your immediately better off as you've got much less ground speed to loose. At a lighter 16,000lbs and 30 kts (Not uncommon down here) I'd be leaving the flare to 100' or so. (A 60' rotor's got a lot of stopping power)
I'd consider it criminal not to practice auto's regularly as much as handling practice as to prepare for the event (Cross fingers). It will also give experience of different conditions/loads rather than just practicing occasionally in one configuration.
I'll never forget the couple of hours mutual practice engine off's in the Gaz on instructors course. Its amazing what you can avoid by bleeding the rotor speed down in the flare (Runways/runway lights/fences....they ought to sell tickets for it!!)
