sispanys ria sez:
Another example is the Piaggio avanti which is using 47 % of the available thermodynamical power of the PT 6 (850 shp out of 1800 thermodynamical hp), giving a flat rating of ISA + 37, meaning it won't loose power in very hot environment.
That's not too unusual as turboprops are upgraded. Turbomachinery improvements provide much more available SHP, but the gearbox becomes the limiting factor, resulting in flat rating up to a remarkably high OAT. (There are Vmc issues as well that may hold SHP to a legacy limit.)