PJ, I broke my HPI S25 engine in last February and it has been brilliant, the cold weather break-in didn't seem to affect it at all. One thing I have done for winter running, I change the body I fit to one that doesn't have any extra window vents cut out. It may only be a small difference but it stops any wind chill from cooling the engine too quickly.
Come to think of it, my first NT16 was broken in during January and it lasted two years before the compression gave out.