I would suggest getting in touch with your Bell Helicopter Tech Rep....or the Corporate Office and ask for assistance with those calculations and airspeeds, etc.
They should be quite helpful I would think knowing their reputation for Customer Support.
This RFM indicates 70 Knots as being the Best Rate of Climb airspeed, allows for a droop of Nr to 97% in transition from AEO to OEI and upon archiving Vbroc of 70 Knots....increasing Nr to 100% but maintaining OEI engine Limitations.
It does mention reducing Airspeed to remain within OEI Engine Limits.
A thought would be to look for Best Angle of Climb airspeed which would be slower than Best Rate of Climb Airspeed as a number to consider.
I suppose one could also consider looking at Take Off Safety Speed too.... just as a Bench Mark for a very bottom number.
http://www.maunaloahelicopters.com/l...copter/412.pdf.
This particular RFM might not apply to the aircraft in question... ensure you use the correct RFM during your investigation.