In a couple of weeks I'm going to ride a relatively new event called Son of Death Ride, which has the motto "that which doesn't kill us, makes us stronger". Nice. This ride is also billed as the toughest one day ride in the U.S. So be it.
Here's the ride profile, it is out and back, for a total of 138 miles and - gasp! - 17,352 feet:
That first climb is from 3,500' to 9,000' in 16 miles, which works out to about 7%. Ouch. At that summit you'll be 16 miles into the ride, with 122 miles left, and already toast. I'm looking forward to it already.