It's always helpful when people use a common language to discuss things. For road steepness, that's grade in percent. Sure, it's technically possible to use centiradians from vertical, but it's not reasonable to expect other people to participate in a discussion when you use that kind of odd terminology.
The best I can figure, the Vesuvius grade averages 10% for 3 miles. That's based on GPS, bike computer, and topographic maps. It's built like most old mountain roads, so I wouldn't be surprised if there's stretches of 15% or more embedded in that 3 miles.
Lookout, KY was perhaps the worst grade going west. I don't remember the numbers off the top of my head, but it was rough. And we just had to laugh at the series of U-shaped dips southeast of Irvine, KY.
Back to the gearing question, pack light, gear low, and get a good running start on the flatter 8% sections to tackle the next 100 yards at 12%. And there's no shame in walking.