Thanks for posting this! 🙂
I would have said 20, but you beat me to it. I'd say the entire highway, end to end, but you've already picked the best part.
532 up Mount Baker for sure. The Chumstick Hwy outside 11worth. The Mountain Loop, I'd say the whole thing but many will disagree about the section from Granite Falls to Darrington. If unpaved roads are eligible, 5400 up to Slate Peak from Mazama. Icicle Road.