Thanks Matt.
My thinking on lowering engine rpm is in reference to R Bedell's reply on the different diameter's between the electric and manual pto pulleys. If the electric pto pulley is larger, it'll spin the deck at a faster speed. Therefore, a lower engine rpm would keep the deck within its intended operating speed. Plus, it has got to be easier on bearings and such.
So far as the engine, I understand the concept of having moving more air across the cooling fins of the engine. I would think that working it at less than WOT would contribute to reducing the amount of heat generated. So long as the engine wasn't operated at such a slow speed that the amount of cooling air was reduced beyond what was necessary, I'm thinking it would work.
Since I've got a Cub that needs a mower deck and a deck that I would much rather store under a tractor, I think I'll try it and see how it works. Besides, the grass is starting to grow.
My biggest concern is to why CC would put a wording like that on the mower deck. R Bedell, I think, has addressed that question. Now, the only thing left to do is give it a whirl!