A few things.
vs. Jets
The PC12's cabin is larger than most jets in that cabin class, so the PC12 will give your pax more comfort, minus the prop noise. Not to mention the smaller fuel bill!
The PC12 has better all round performance (minus air speed of course) and when you look at the 850's economy cruise of 252kts you've lost all advantage. So you get better passenger comfort, better payload, better STOL (think it beats it by around 200feet).
AS for running costs, I'm not sure, I found a pdf on pilatus's site (
http://www.pilatus-aircraft.com/medi...-The-Facts.pdf) with some facts and figures, but why not contact someone like the RFDS and ask nicely, they are one of the biggest operators of the type in the world!
I would always perfer to have more range and be able to throw more stuff in my a/c than have a little extra speed, because the 30-40kts and say 12 or so minutes you might gain on your average flight from the faster a/c will soon mean SFA when your IMC with a nasty headwind when your clients desides to take the wife and kids on a holiday in the company plane
