First of all, my Kubota is a gear drive model. Now, i didn't say "always". I did say when you have a load on the PTO!
Does it say in your manual they are talking about PTO work?, with a load on the engine?? That "does" make a difference!! There use to be a lot of skid steers than ran Kubota engines, and you ran them wide open. My Grass Hopper mower is Kubota powered, and you run it wide open, and what about all the Kubota powered refrideration units that are run wide open???
Trust me, if you have a load on the PTO, run it at PTO speed!! You don't have to on yours, but you are shortening the life of your engine!
Robert