I've been messing around with recording pool matches with my Hero3 also. I'm waiting on my 2.1Amp USB power adapter to continue testing since the battery life is not very good. I like having the Wi-Fi enabled to control the camera w/o touching it and that kills the battery.
If you don't want...
Banditgrr: Do you maybe have the Hero in the protune mode? That is available in the settings. It records at a lower compression rate/higher file size.
You enable/disable protune from Settings -> Capture Settings -> ProTune.