There's no easy answer. I'm very good with cumulative climbing in roller coaster terrain, but absolutely detest long sustained climbs.

What people can handle depends on what they normally have to handle, ir. where they live, and the nature of the climbs themselves. As for myself, I have to go out of my way to climb a total of 2,000 feet in a hundred mile ride, but if I really look for it, I can probably find about 5,000' or so, ie. 15 climbs of over 300'. Otherwise the highest single climb near here is about 1,000', and getting there and back would involve another few thousand feet of roller coasters.