That is a fun ride event, I have done it several times in the past (although one year it was snowing at the top and shortened, and the ride up was among the coldest, wettest, and most miserable rides I have ever been on). This year I'm domestique-ing my wife's ride on that weekend (Bike MS Deception Pass ride) by staying home with our 5 year old.
Have you done this climb/event before, or climbed similarly long, sustained grades? Below is a photo looking up to a switchback from a previous year. The views are amazing and its nice to have the road closed to cars for the event.
