just trying to better understand the normal power variances between IGE / OGE / S&L at some standard speeds (55, 70, 100, 110kts), etc., to develop quicker / better power margin assessments
When flying the Bell UH-1B the military operator had a very nifty means of determining if you had the power available without resorting to charts. You first checked TQ required to fly S & L at 60 knots, and then pulled power until you got rotor droop and noted that TQ. From the difference between the two TQ readings there was a simple gouge as to your capability. The reading obtained would tell if you could HOGE, HIGE, zero/zero, or running landing. Simple and effective, though forget the figures now, too long ago.
If this was a relevant chart it would be in the flight manual
I'm sure that a necessarily experienced engineering/test pilot could develop a similar gouge for a Robbo.