Las Vegas to Portland — two options, which would be best? I'm worried about Siskiyou pass in the dead of winter

In about a week I'll be driving up to Portland, Oregon, from Las Vegas. I've driven the route many times, but never in the dead of winter. I always take I-5 because if something happens to my car it's easier to get serivce, and becauase I make it a three-day trip and there are most places to sleep. However I'm worried about the conditions of siskiyou pass, so I'm wondering if anyone has had any experience driving it in the winter? How bad does it get? Should I go through Reno and up the back way instead?