When I lived in Denver with the Keystone/A-Basin season pass, I always took the Silverthorne route. Exit 70 through Loveland Pass is a narrow, two lane road with lots of hairpin turns. With the slower driving speed due to the switchbacks, it didn't seem to save any time to Keystone unless there was a traffic jam near the tunnel. Either way, it never seemed worth it to me to monitor the conditions to (maybe) save a couple of minutes, especially when through Silverthorne was such an easy straight shot.