I took I-40 last year at the end of December, stay overnight in Moriarty, NM. Woke up at a snow storm that had closed I-40 form Santa Rosa to Gallop. NM. I wasn't towing or driving an RV either. 15 MPH the entire way. So what I'm saying is, if you decide on I-40 that time of year, good luck.
Now as for I-10 goes, it's the southern route that most people who travel this part of country in winter take. When was the last time you drove thru Phoenix, AZ? It's a total nightmare. So here's my route to keep you out of the nightmare, take I-8 over thru Gila Bend (the Phoenix by-pass route). Go west toward Vicksbury, take hwy 72 and head north to Parker, AZ. From Parker, take hwy 62 to Vidal junction, then hwy 95 to Needles, CA, back on I-40 west for about 10 to 15 miles, and get on California 95 north all the way to Las Vegas.
Now if you want some real fun, from Buckeye, AZ take I-40 all the way over to Quartzite, Az. THis time of the year there's a really big get-to-gather. It's where all the RV nuts go in January. I've never been there because I just kind of stay away from 100,000 or more people out in the Desert.
