Some limitations are inherent with each chipset and the SDK, so to get less than 30% could require making essentially a whole new cam. I'm happy with running a 128GB card as a work-around as they're relatively cheap ATM. I was getting almost 7 hours regular recording with a 64GB card, haven't really checked the bigger one.
My g-sensor worked perfectly in my smooth-riding minivan but not in the workvan (which rides like the truck it is). Earlier ones had audio issues which I think was improved, but even with all this IMHO it's a great cam for the price and to get much better than this will cost you around twice as much. I'll be getting more for side-cams this spring when I 'finalize' the cam setup in the workvan.
Phil