peak HP vs continous HP is probably the bigger issue. It's like comparing PMPO watt ratings on amplifiers to RMS ratings. Saws are generally rated for continuous load, while things like bikes and go karts are rated for HP at a low duty cycle. Look at it another way - take an engine out of a car and marinize it and put it in a boat, and it loses a lot of HP! Cars are revving up and down all the time, but they have a low duty cycle. Boats are the equivalent of taking a car and running it up a steep steep hill in 3rd or 4th gear at full revs, and then doing that continuously all day long. If you had them tuned for max HP, they wouldn't last very long.
'industrial' type engines are generally rated for continuous full load usage, which is an entirely different beast from most engines. You can get the exact same block from cat in a range of HP ratings, with accompanying reduced duty cycles and rated engine hours until failure as the HP goes up on the same block. Step up to a bigger block and you can have higher duty cycles and longer engine life. No real surprises there, something that pretty much everyone knows. A chainsaw is made to run long, and continuously loaded.
If you can actually make enough money on an 880 slabbing for a week to pay for itself almost twice over (really? $5k a week?) then put that toy on the shelf and get yourself a bandsaw mill. Or sub some of your work out to me. I'll gladly do a week of CSM'ing for a mere $2500. I'll even supply my own saws, chains, a 7 tonne truck, fuel and oil. You can keep the other $2500.
There are many many bandsaw mill options out there, all of them fast, efficient and with minimal wastage. You'll get a lot more slabs done in a day and can probably pickup more work too. There are portable options available, which can be setup in the woods, as well as trailerable options and massive workshop sized units. They will all give a better finish than you can achieve with a CSM and in less time.
Shaun