It seems to me that you are really buying into hype and myth far more than reality.

I-84 does have some difficult stretches, that are more challenging than a typical interstate. However, if you read the article you linked to yourself, you'll note they actually have more problems on that interstate in the summer than they do during the winter, and the reason is simple - nearly all of the problems are caused by drivers ignoring warning signs and going too fast for the conditions.

It is true that I-80 can see high winds, and that can make for challenging driving conditions, but driving at 10,000 feet has it's own set of challenges. I assure you that for every problem you've found on I-80, I could find something similar on I-70.

Finally, in regards to I-90, you've bitten hook, line, and sinker into the single biggest myth of winter travel. Despite what you're thinking, North does not make for a more dangerous or more snowy drive, and saying south does very little to improve your chances of good weather. Again, there are many, many times where I-90 is a much better winter route than I-80, I-70, or even I-40, especially because it stays at a lower elevation than all 3 of those other cross country routes.

And again, the most important factor of all is the actual weather forecast. As you noted, you're comfortable with I-70 if roads are clear and dry. If roads are clear and dry - then you've got nothing to worry about on any of the routes you could take. The question really comes down to which roads will be clear and dry, and you'll have to wait a few days yet to figure out which roads those will be. The point is that if I-90 is forecast to be clear and dry, while there is a storm moving through I-70, I-80, or I-84 then it would be silly to dismiss I-90 because it is farther north. Similarly, if I-84 looks clear, then there is no reason to add a few extra miles to go up to I-90. It's the actual forecasts, and not fears based on what you think has happened in the past that should be guiding your decision.