Trying to tell you an average speed is simply pointless because we can't possibly tell you what the conditions will be. In good conditions, 55-60 is pretty typical average speed on the interstates, once you factor in minimum stops and slowdowns. On 2 lane roads, you're looking at 45-50 most of the time, but if you're seeing bad weather, those numbers could be cut in half, or worse.

I'm not sure where you heard you can't put chains on a 4 wheel drive vehicle, but that's not true at all. With AWD, you do need to make sure you've got them on all 4 wheels, but you certainly can use them. However, there is the element that if the roads are so bad you need chains, and you have little or no experience driving in snow, then you probably will be better off stopping and waiting for conditions to improve.

The reality is you're talking about a winter trip to the mountains, we can't tell you what kind of weather you'll see. If the possibility of having to drive in snow seriously stresses you out, then perhaps you would be better off finding a different destination, because snow certainly is a possibility that you have to be prepared for.