I doubt if it is going to be that much quicker, i don't have any time in a 200, only a B100 but I suspect it trues around 260, and a 500 is around 320. I was never that concerned about economics of it I just flew the airplane.
The thing to look at is how much load do you want to carry? I think you can probably fill the seats on a 200, but if you try that in a C-500 you will be over ZFW unless they have the increased ZFW mod on it, which adds about 1200 pounds, but then you are offloading fuel.