Hi Steve,
I have used Innov K2s on previous bikes and currently have a K5 fitted to my bike. If its just dash cam footage you require then the K3 will be plenty good enough and an easier install. but if you want Gopro quality footage with decent sound then I recommend the K5. Installation is a bit more difficult but the image and sound results(depending on where you mount the remote mic) are really good. I mounted the main camera under the front beak and managed to get all the connections up by the headstock to make a neat install. The rear camera went under the rear rack along with the remote mic to give decent exhaust sound. A 512 GB SD card gives a full days riding footage and some.