I'm actually thinking of buying one of those
car black-box recorders that simultaneously record speed, GPS position and record video/sound. (could possibly mount it below the headlights, between the forks)
I'll have to make a waterproof enclosure for it, but if it's as good as I've seen on the telly, it'll be better than just a GoPro, which to see speed, you have to have mounted on the tank - and I've got a tinted double bubble 'screen, so that wont work!
There are several cheap options for those, as well - but you get what you pay for!
BTW - gees it looks like that camera gets close to the ground, and it didn't even really look like you were leaning!
Cheers,
Rick