I know the PT-6's in the 90's I flew burned about 600# and hour at lower altitudes and maybe 450-500#/ hr in the flight levels...... Cruised at maybe 210-215 indicated down low, and maybe 170-180 at FL200 (roughly)
Climbed at maybe 1500 ft/min up to 10,000' and reduced to maybe 700-1000 ft/min up higher...
Again it was only the C-90A/B models, so a 200 or 300 is definitely a lot better... Overall I wasn't that impressed with the speed of the 90's.....But it was a good work horse, I never had a problem in 1000 hrs....
One thing I noticed about the 90's also was that the brakes were pretty weak.... Although just based on it's 100-110 knt REF, it could get into some shorter fields, the brakes didn't do all that well getting the plane stopped really short.
I think maybe for the typical amount it costs to charter a King Air, people wouldn't be willing to buy into it as a Fractional a/c. King Air's are relatively expensive to buy... I think you could buy a smaller Citation for almost the same price as a new King Air. (could be wrong, I've never really compared the $$)