I carry a 5.5" Ruger Bisley Vaquero's in 45 colt in the bush as well as use it for Cowboy Action shooting. I have not used the Sheriff's model but my experience with the Bisley(which is only really a grip difference)is that they are very good guns with just about any load that you can find or load. I don't think that I would use a cowboy load which is a little slower than I would want. I would want to have a 255gr bullet at a velocity of about 950fps to 1000fps which should be very managable in the Sheriff's model Vaquero.
Cam