The actual drive time is of negligible difference.
Sunday traffic on I-70 is always bad. In good weather, you can beat the traffic if you leave the parking lot no later than 2PM. That may or maynot be enough time for you to catch your flight. It's all weather dependent, the airport, rental car return, security status.
Berthoud Pass adds a few perks. January is prime wind season. Strong winds and blowing snow can close the pass. There are several major avalanche paths to be crossed. They only cover the roads a few times a season but the road does close for avalanche control. As avalanches come down over I-70 and it gets closed for control too, that's not a new variable either.
You should come give us a visit.