Thinking of upgrading to an iPhone 4 (from a 3G) for the HD video camera, but don't know which capacity to get. Can someone give an estimate for how much space a recorded video takes? Like 5 mins of HD = 2GB or something like that. I've gotten by with just 8GB with room to spare but with an HD camera I don't want to get stuck with 16GB if my usage fills it up fast. Thanks.