Yeah, I would not want to chance doing I-70 in Colorado in December. The long climb up westbound to the Eisenhower, and then two long descents, the E and the Vail Summit, might be a bit dicey.
HOWEVER, once past Vail, the road is not so bad. We did it E/B a few years ago, and I just remember it was a leisurely slow climb up from Grand Junction neighborhood. We stopped at a nice Walmart in Rifle on our way east. If you can get past Vail because of a good weather forecast, then the rest of the way west is pretty easy - no great climbs or descents from there to Utah. You're up on a high desert plain,and it's actually kinda boring from G Junction to Moab, if you're headed that way. We did Arches, etc and then went up Utah 128, a "scenic byway" to catch I-70 east to home. I just remember that I-70 in eastern Utah and far western Colorado was just flat and straight.
Oh, and depending on your timing and all, make sure you don't do Glenwood Canyon in the dark! It's midway between Vail and Grand Junction, but has to be seen to be believed.
All of the above, of course, is predicated on decent weather. If it's snowing, all bets are off. :)