Never trust the manual 100 percent. I have a KX41-3 excavator and the manual contradicts labels on the machine. Manuals are often written in one language then tranlated inaccurately into english. Anyway as far as mowing is concerned I adjust the speed according to the load the mower is faced with. Light load 2000 or sometime less. Heavy tall wet grass 2600. The higher RPM does lift and toss the grass better I like to save a few fuel bucks by running at a lower RPM when I can.
I usually take a little off of full throttle.