Main thing IME is leg fitness. Can you do a ride of say 60 miles, 3000', where you do every climb in your sweet spot, all the way to the end? Can you do long steep climbs, say 10-12% one after another? Some of these climbs are simply one steep ascending roller after another, no downhill between. Those are leg killers. The average slope is not a problem, just the the rollers being maybe twice as steep as the average. Bring low gears. It's the ability to repeat. 85'/mile can be no big deal as long as the climbs are a steady 6%-7%. Steep rollers taught me the meaning of Jens' "shut up legs" motto. I learned to suffer on my first 300k, though it was only 10,000'. The steep rollers got to me.
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