Sweet ride. That sounds hard as all getout. You must be in solid shape to find climbing at elevation with a 12% half mile finishing stretch to not be as bad as you thought. I'm gonna do that ride someday soon, but you better believe I'm going to be training hills, hills, and more hills in preparation for that one.
I can't believe that 500feet is bigger than the typical hill you climb. 500feet around here in Norcal is a good sized roller, but not a mountain climb! Goes to show that power is power and if you're practicing putting up big numbers on the flats, you'll be doing the same on the climbs.