3.1 is fine for a cutoff. 3.2 gives a little more safety and doesn't push the batteries as far. A cutoff of 3.5-3.8 is nonsense, I can easily put enough draw on a pack, even a good pack to drop it down that low during a run. Driving style plays a big difference in runtime. For starters, is he flipping over a lot. A poor driver can have more play time just as easily as a good driver. If he's upside down more than he's driving he could get more time. Without running the numbers I'm nmot sure but your gearing seams pretty high. Also you don't have his gearing listed. He could be running his more efficiently than yours with optimal gearing.