The longest i've recorded on my Liquid image is an hour and it said I still had half battery remaining. I have tested it in the car and it will power and record at the same time so I guess you could set it up that way if mounted to the bike.
I have not tested if it will record over previous files (don't think it does from memory) but with a 32gb card in it I doubt I will ride long enough in 1 go to find out.
Thing is they are cameras designed for different reasons, the Ego is for capturing general purpose action and this is highlighted by all the add-ons you can get for it. The Roadhawk is meant to be a safety device with the time stamping etc.
For me personally I will stick with the ego for my home movies of trips away.
Both good cams just depends on your use.