Hello !
In August I cycled the World's hardest climb and I've just finished editing a video for english users, english speaking people :).
Mauna Kea is the most difficult road bike cycling climb of the World based on the data of salite.ch and climbbybike.com, the two most serious cycling climbs's collections. It's an epic climb, a monster !
Mauna Kea has 2 ascents: the Hilo side is harder than the Kona side ! Both starts by the Pacific Ocean (Big island, Hawaii) and ends just at the top of the 4205 m high peak. The 1st 50 km long section is not too hard: the average steepness is below 5% (for more than 2000 m heightdifference), but the last 20 kms has 2000 m heightdifference that means 10% steepness; the maximum grade is 17-20%. Other difficulty is the thin air above ca. 3300-3500 m (at the top there is 40% less oxygen than by the ocean) and a 7 km long gravel-sandy section above 2800 m.
At last there is another thing to made it tough: there is only one place to get water, buy some snack, drink: the Visitor Center after ca. 55 kms at the height of 2800 m. That's why that when I left the ocean, at sunrise I carried ca. 5 liters of water.
In the last hour of the daylight several cars go up to the summit to enjoy the sunset.
Because I cycled all of the paved climbs finishing above 2000m in the Alps, Pyrenées and Canary islands and cycled up to Pico Veleta, I had to say that it is really the toughest cycling climb of the Earth; it was harder than any other climbs that I cycled before, much harder than Monte Zoncolan, Grosser Oscheniksee, Speikkogel, Angliru, etc.
Have pleasure with it and hope You like it !

Gábor
( http://www.facebook.com/cycling.high )