I-40 can be a smooth sail with some cold days or it can suddenly become a 2 day parking lot in the freezing snow.
Taking I-10 is longer but will avoid most weather concerns so long as you can stay awake along certain parts of that route.
You know your comfort level.
I do agree with Captain Happy to use I-8 at Casa Grande to avoid Phoenix as the South Mt. By-Pass in Phoenix won't be completed so you'll have to transverse the heart of metro Phoenix. You'll be dealing with all the business tourist at their conventions and golf courses flinging around in their rental cars like lost puppies plus every single snowbird who should have had their drivers license revoked years ago will be on those same roads clogging things up. I-8 gives you a couple of alternatives to the potential mess going through the metro area.
