That's a lot more individual than the aggregate study results generally indicate. I'm a cranker, not a spinner, and I used to do 250 miles/week -- that included a "century Sunday" -- with little fatigue (no more than I was looking for, certainly). Most of the folks with me would be turning at about 150% of my rate at any given point. I tried the 90 cadence, and it just didn't work for me; I'd get pooped over a piddling 20-miler, and never really improved in endurance.