well, a few things:
- if you don't feel that you have a lot of control at high cadence, that either means you need more practice or you're really using too easy a gear. you get better at it when you practice and concentrate on keeping constant pressure on the pedals despite the high cadence.

- i understand the impulse to use harder gears and "hammer" - you asked if there's a risk of injury. I learned the hard way that "hammering" all the time can cause injury. You're likely not *pulling* anywhere near as hard as you're *pushing*, which means you're using your quads a lot. contraction of the quads pulls the knee together, which puts more pressure on the meniscus, which can lead to knee injury.

so, that's what happened to me. hammering all the time led to knee injury. lately i've been concentrating on keeping a higher cadence, which has given me the control to apply force better over the entire pedal stroke.

not saying you shouldn't use hard gears - you gain muscle that way - i'm just saying don't overdo it. i regret it