I would recommend keeping your cadence, as the fitness you gain with this higher cadence will be more valuable down the road. Especially on long rides, low cadence will wear you out and is hard on joints. Also, if you can keep a certain amount of power at low cadence, you can definitely do it at high cadence too, you just need to get more comfortable with the faster pedal speed and let your body adapt to it. By training your body to be efficient and powerful at high cadence, you'll be a much happier and healthier century rider
-Trevor from TrainerRoad