If by cooling problems you mean it never gets hot and you have to keep it all shut up to get some heat in the thing -then that has been my experience too!
The IO550 equipped 210 I have flown was a beast. If only they all had that sort of performance! Because lets be honest- a 10,000hr 210 with a tired IO-520 in it doesn't give eye watering performance out of a bush strip when its 40 degrees!
In terms of describing a 550 210 as skittish- perhaps they were testing the install in a pre-M model with the lower gear and flap speeds? The one I flew was an L model with the lower speeds, and on a long descent you needed a few miles in a level segment to get it back into the acceptable speed range to start dropping things!