I'm curious about URP, too. Even though I have a keg, it doesn't get cold here, so I can't simulate winter hunting conditions up on the rim.
FWIW, it looks to me like something's amiss with your chrono results. It _does_ get as cold as 45 here sometimes, and my Re-17 Creedmoor loads don't slow enough to mention at that temp, nor has it been like that for anyone else I know who has tested it.