Depends on how big the brush is that you are chipping. You can always give it a try. If it bogs tractor down too much you may want to run straight 540. The 540E range is nice for light duty work like pulling a finish mower or light bush-hogging, but if it's going to get a work-out, you should really use 540. IMO there is more damage done to a small diesel engine by bogging it down than by setting it at a comfortable RPM for 540 PTO.