This is the camera I use. The only complaint I have is the light exposure the review mentions. It adjusts to the light conditions very slowly and when it is very cloudy it seems kinda dark. When the sun starts to set you won't be able to capture anything. I'm not sure if that is the same for the other cameras. But the thing is bombproof, secure when mounted, tilt angle adjustments on the fly, and very easy to use. The buttons may be a little hard to push but you get the hang of it. It comes with every mount you need. But it works better with just velcro and a flat area on your helmet. I grabbed mine cheap on ebay, new too. I would give this product 3.5/5 stars.
The 5k looks great but like you said heavy. It's also more expensive and once you test the camera a few times you will get the hang of how to capture the video best. Sometimes I just take off my helmet and shoot the video that way of my friends.
My latest video I put together is in the Rutgers Ecopreserve threads. Check it out if you haven't already. I also have a diablo thread somewhere. It was really sunny that day and the video turned out great.