I always like to train at a higher cadence, train for speed and get power as the saying goes. Everybody has an ideal cadence, the 'sweet spot' on thier throttle. Mine is around 75-85(relatively low) but the lighter you can load your legs the longer you can ride without soreness. In races I alway have better luck revving up to a higher cadence on climbs than trying to power out.
The idea of the gears is to do all you can to remain in your ideal rpm range(like a car does as well), thus being the most efficient. Periodically when you train, ramp it up to a gear or two higher than normal, you may be surprised at your improvements. After a while you will be able to sustain those pedal speeds in the higher gears. That means you have more power
Most of all, have fun.