I've seen the very same Tq to N1 transition in BH206s and BH407s at roughly the same altitude. Almost always starting at MGTOW on 1-2 hour legs, what works for me is the gentle climb ShyTorque mentions until reaching a temperature or Vne limit then reducing power as necessary. Roughly 6000' works well as a practical enroute altitude finishing with the same cruise descent.
Bob