I've done that climb a couple times, once on a rental and once on my own bike. The rental was a Roubaix from West Maui Cycle with a 50-36 compact double. I want to say 12-28 in the back. My own bike was a standard 53-39 with 12-27. Either way, you don't need super low gearing. Nor do you need electronic shifting as you're going to spend the whole day in a few gears. It's a steady 6% to the top and I don't recall anything where I needed a 1:1. It might be nice to have discs if you do the ride down, especially since it can get wet. Biggest hazard on the way down is the tourists on cruisers who get driven to the park entrance and coast down. If you do ride down, either carry a windvest, gloves, and arm/knee warmers or have someone meet you at the top with them.