Everything is important. Hydraulic horsepower is nice but it requires engine horsepower to create HHP. My FTX-140 is rated at about 240HHP that is 100 HP more than the engine creates. But it requires an engine to turn the pumps, as you know hydraulics can be multiplied, how else could my 110lb wife help jack up my F-450. One issue that you left out is cooling if you are grinding dense material you will keep the engine and hydraulics at full cycle. If it is available on your machine get a reversing fan! I had on on my ASV and it kept everything clean as a pin. I have one on the hydraulic cooler on the 140 but the engine cooler does not have one, I have to pressure wash my radiator every two days in because of the dust out here. Good luck on your venture.