Most pumps are designed to be run at full tilt all day and so shouldn't be affected by this.
Indeed, running a pump at less than full revs wouldn give you less than the pressure or flow you are expecting.
However, as your pump is a little underpowered to be running 2900 psi, it would probably not be good to run it for 8 hours a day.
Regarding 'breaking in' a machine, as long as you service it according to the manufacturers recommendations, you should not have a problem (mainly oil changes).
Andy