I'm not a big fan of the Hero camera system because of the extreme wide angle of its lens along with the associated fisheye distortion, and no extenal mic input. I do understand however that they might make a version with a straight wide angle lens. An external digital recorder synched to your video is the way to go for best results with sound. Using a simple foam windscreen for the mic will
not work. A special mic setup must be used. Below is a test I did for audio using a special mic setup I designed. The speed reached during the first acceleration was around 90 mph and there is no windnoise, only tire on road noise. The recorder was a Zoom H4 which caught the snarling and growling of the sidepipes well. The video was recorded with a cheap point-and-shoot camera using a conventional wide angle lens. Notice the horizon is straight, not annoyingly curved as a fisheye lens will cause.
(If folks are interested I could probably put something up here showing how the mic was built and the setup was done, but it would take awhile to put together a presentation)