Wife and I took our toughest ride to date on our new tandem: 39 mile loop with 1800' of (GPS) climbing. I'm never, never again going to give a thought to changing the cassette for closer spacing on the tandem (maybe in my next, younger life). We would have been fine after stopping at a McD's for gigantic lemonades at about the 28 mile point, but the final 10+ miles were dead into a 15-20 mph head wind resulting in a 10-11 mph crawl.
We had a 31 mile loop with about 1600 ft. of climbing 3-4 days ago, but there is absolutely no comparison between the two rides leading to the conclusion that there is more to a bike route than can be expressed in a single number. The climbing part of this route was part of the Tierra Bella 100K and Century, but didn't seem quite so steep on our singles.
Fortunately, my wife doesn't look in on BF since she would kill me if she knew about the "wife eating a granola bar" picture. Vista pictures are from the top of Canada Road in Gilroy, CA.