Rode N-S on the GDMBR (supported, I’m old) from Canmore to Antelope Wells last summer. The legendary descent down Fleecer Ridge (south of Butte) terminates at, reportedly, 37%. Stupidly, one other rider (a tough 69 yo Aussie racer, yes still races-sponsored by Santa Cruz…take a bow, Ray) and I on my 3.0″ wide summer rubber, rigid, fatbike descended with both wheels locked up the whole way, groin firmly behind the seat post (except the middle third when my baggies got hooked on the saddle nose)…would have been less of a white knuckler with my current Bike Yoke dropper….keep in mind, the folks traveling S-N have to ascend this 3/8’s of a mile serpent.
Still on the official GDMBR (N-S) north of Steamboat Springs (where I live) between North Sand Mtn and Meaden Peak, on FSR 42 is a pretty brutal 4 mile heavily rutted, jeep road climb. The last 2 miles has some very steep sections all at about 9000′. Self supported beasts with 20+ lbs of gear manage to do it all without stops or wobbles (but it is bad enough without additional gear for me).
(and yes, since one mentioned Stormpeak….Stormpeak challenge from above the gondola is a doable grinder, particularly the last 300 meters of heavily rutted, steep double track to the Desert Research Institute weather station, ~10,500′, beginning just beyond the intersection with the Mountain View trail at the top of Bar-U-E lift).