Capt. Notarious,
Its not so much about the power but (as Mama Mangrove correctly stated...) its all related to the fuel burn.
If they could, they would probably fit the PT6 and be done with it. Canadian motors rock...
However, an S76 or a 155 are going to suffer a dramatically reduced range and be economically impractical. Hense the reason that the S76B model is largely a corperate machine these days. It has the fuel hungry engines.
The other issue is that big motors weigh more, cost more and can lift more. Larger motors will encourage the customer to ask for more payload and any advantage of the power surplus is soon absorbed in payload increase.
EG: The C model 76 has the 1S1 and has always been N1 and temp limited. The solution for this was the 2S1 engine in the C+. Better OEI and hot and high performance...
Does anyone know the operating specs of the C+?, the MAUW of the C model was 11700lbs. Any changes to that?