For the past couple of years I've been using a pair of GoPro 3+ Blacks. Very easy to power a multi charger through USB, storing it in the tank bag, and also run a permanent power cable to them if I want to. Although, thanks to the unique way GoPro design their cameras you then can't record sound via an external mic at the same time unless you use GoPro's ridiculously overpriced splitter cable, and that's pretty hit and miss anyway.
I've had enough of the bulkiness though and have just decided to switch to a couple of GoPro 5 Sessions. One of the chaps on our last tour had the original Session, and thanks to the more simple auto power off unless you're recording he was able to get his to last a whole day by just recording the bits he wanted rather than accumulate hours of dull footage that you then have to wade through later on.
I do like the smaller form factor of the Hero 5 Session, especially for a helmet mount (the new ball joint is very good) so hopefully it'll be up to scratch for this season's riding.
It certainly doesn't get you around a need to swiftly delete footage though. The best solution for that is not to record it - it isn't like you're likely to risk posting it online anywhere afterwards