Currently my cameras are a Contour Roam3 on the helmet and a Fly6 on the back.

Just a warning, you WILL NOT be able to read the license plates of a car blowing past you 30+ MPH over your speed. I doubt even with the latest GoPro Hero Black set at 120 FPS (and those are $500). The bitrate just isn't high enough to do it.

Audio while moving is always going to be a loss. Some cameras have usable audio when you're standing still. Usually if you have a camera where it has to be inside a case to be waterproof, the audio will be zero inside the case. The Contour Roam3 and Fly6 are both waterproof without a case, and they produce OK sound, though still miles from great.

My minimum criteria for cameras are, 3 hours runtime, waterproof, relatively lightweight, reasonable mounting systems. GoPro fails on both battery life (though the newest may just BARELY qualify) and reasonable mounting (seriously, there's no elegant way to mount a brick).