When working hard(hogging, loading, digging, pulling a grader, etc) I always run between 2300 and 2500. When I have the PTo wood splitter on the 3 point I run it at 2000.....I never even move it unless I am at 2000 rpm. HSTs' love rpms and running up at the upper end just makes it work better inmho.
This is totally different from a gear or shuttle tractor, and one reason why many old timers just can't adjust to a HST tractor, they are just pavloved into loping around at 1500 rpms all day long.