I'm sorry, but you can not say that I 70 will be "less icy" than I 80, [or any other Interstate at any particular moment] only the weather can determine that and we all know how unpredictable that can be ! As stated earlier in this thread, only up to date weather forecasts and road conditions can give you the best chance of avoiding poor conditions.. It will help to save a lot of time. It will be less icy as well.
There is a good chance that this trip is already underway, so good luck !