My first race of the year is a mass start 105 mile race on hilly dirt roads. The hills will be under 400 feet, but steep and frequent. I plan to ride a Trek X01 cyclocross bike with 46/38 x 12-27 gearing. Based on my experiences with similar courses, one thing that concerns me is that I won't be able to maintain my self-selected cadence on the hills in a 38x27. I don't think the Shimano 105 rear derailleur will take anything larger than a 27 and finding replacement front chainrings seems troublesome. So any case, I'm wondering if I should a) try harder to change the gearing, b) train a lot at low cadence or c) don't worry about it. Any thoughts?