There was supposed to be about a 5hp difference between the 9N/2N and the 8N due to an improved head on the 8N. I too have heard people complain about HP differences, but I'm not sure we would notice much of that at this point in our N's lives. I could be wrong, but I think quite a lot of this has to do with a poor regular maintenance routine and general engine wear.
I would happily stand corrected...
PS: You were warm this morning! We were -4 in Long Prairie at 9AM :-)