For today's Sunday training ride, I decided to keep it short but intense, so it was just 20k, but with 10 repeats of a
short nearby hill that averages 5% but has stretches steeper than that.
My target climbing pace for Haleakala is 10 kph, and it would appear that right now I'm able to maintain that on a similar/steeper road for about 5 minutes - so with a modest 70x improvement I should be right in the ballpark.