Just curious, are you running same size heads? Or how are you comparing the class 7-8-9?For whatever reason, class 9 are the most popular in many parts of Saskatchewan. In Alberta class 8 seems to be the most common.
It's interesting how nominal conditions vary across the provinces. For me a class 8 just burned more fuel than a class 7 with no additional capacity. Class 9 would be similar for me. For others not too far away class 9 is not enough power.