I just returned from Maui were I did the Haleakala climb (ascending 10,023' over 36 miles). I had my own bike with me and so was stuck with it's gearing. I was a little concerned that I would be able to haul my 215 lbs up the mountain with a standard double. The lowest gear was a 39 x 25 (~ 41 gi) so in order to keep the rev's up I had to keep the speed up. Early on I was spinning easily at 9-10 mph in the 39x25 or 39x23. As I got higher (above 6,000') I was pretty much stuck in 39x25 with speeds of 7-8 mph depending on the pitch. The grade typically ranged from 5-8% occasionally dipping to 2-4% or pitching up to 10%. The last 1/2 mile my speed dropped considerably as the grade increased to 10%+, which just about killed me at 10,000' (but I stood on the pedals and managed to make it to the summit.) Total riding time was 4 hours 20 minutes.