I've done centuries before, some at a reasonably decent average speed. But just for grins, I'm thinking of really hammering an upcoming event. It will be fairly flat, which should allow a good time. The attendance will be fairly low, though, so I half expect to do most of the ride solo.
Under those conditions, I was wondering what the Fifty+ group would consider to be (a) a good moving average speed, and (b) a good start-to-finish time?