The object is to not use the brakes, and to not wear them out.
I've been down AZ89 from Prescott. According to the comments there's a 1355 drop (4400 to 3045 feet) in 8 miles, an average 3 percent drop, which I wouldn't compare to 7 percent around two 180 degree curves, and then a sharp 90 degree curve at the end of the second one. There is no way you'd be going 90 on those, not twice anyway.
Basically I'd like to know if letting the engine rev up in 3rd gear is okay.