Years ago 3 cycling friends and I decided to do a 5 day self-supported, credit card style touring ride, from Waynesboro VA to Williamsport VA. None of us were racers or high mileage cyclists, but the guy who was in the best shape planned the route. I had done some bike touring, the rest none. The guy who had done the least amount of biking was the kind of guy who is always the most prepared, carries the most stuff.
The first day included a climb up to the Blue Ridge Parkway. Looking now at the Strava
segment, it was just over 3 miles and only 3% average grade, but: (1) there are several stretches of 15 - 20%; (2) we were on loading hybrid bikes; and (3) this was 25 years ago, I'm sure erosion has lowered the average grade since we did it...
About halfway up, the least mileage/most prepared guy released why he didn't really need a spare cell phone charger, a pint bottle of chamois cream, a candleabra, piano music book, etc... Took a while for him to reach the top - the next day at a local post office he shipped home nearly half of what he had been carrying.
On that Strava segment, the KOM averaged just under 20 mph - that was our downhill speed getting off of the BRP. I'd guess we averaged 5-6 mph going up that climb while moving...