With the Sony HDR-AS30V on my helmet set to 1280×720 at 120 frame/sec, the plates on passing cars remain barely readable (clicky for more dots):
Throttling the camera back to 60 f/s produces slightly better results:
The differences seem due more to changing lighting conditions than frame rate: the camera definitely produces better results in bright, direct sunlight.
These are about as good as it gets and, if you look carefully at the images, you can see plenty of compression artifacts that wipe out small details.
Equal-size dot-for-dot crops from the original 1280×720 images, matted together, and very lightly compressed because there’s not much detail to compress…