I am not sure "dangerous" is the right word, as millions of Americans [and visitors] need to go about their business on a daily basis, and do so safely. That is not to say that you don't run the risk of seeing a winter storm, and might have to pull off the road for a while and let the road crews do their job. It is unusual for an Interstate to be closed for more than a few hours, perhaps a day in the worst case scenario, and they are the priority to keep clear.

As you are shipping your car and most likely on a deadline, I would use the 5 nights / 6 day's just so you can relax a little and don't feel under pressure, if the weather is kind you can enjoy a little sight seeing.

Keep an eye on the weather forecasts and road conditions prior to leaving and keep up to date while travelling. That way you can make informed decisions and in some cases, that might mean staying in the Motel for an extra couple of hours if there is a storm about, or getting an early start and make hay while the Sunshine's.