I've done the trip from Tucson to the Seattle area via Utah a few times in our S. However, I didn't go through Kanab. Went through Vegas. Charged at the following Superchargers: Wickenburg, Kingman (for 10 min), Henderson, St George, Beaver, Nephi, Tremonton, Twin Falls, Boise, Baker City, Kennewick, Clu Elum.(Ellensburg the first time, but not now) Never had to wait for a supercharger, and only Kingman was kinda full. Broke the trip up into 3 days- Overnight in Vegas, Tremonton and Kennewick. Made day 3 pretty short. This was in an S 85.
Came back via I-5 one time- I-5 Superchargers can be pretty busy. It was 2 years ago and had to share stalls in a few locations, I can't imagine what it's like now. If I was willing to take 4 days to make the trip, maybe I'd do I-5, but unless the weather is extremely bad, I'd take my chances going through the WA,OR,ID,UT,NV,AZ route.
Did the 101 thing in an Infiniti G35 Coupe a few years ago because I-5 closed north of Redding, had to back track nearly to Sacramento on that trip, added an extra 600 miles to the trip-