I prefer the gforce gates g model. It's not quite as tough as the Polaris OEM or the gates carbon, but I believe it's more consistent performing whether hot or cold. More importantly, it won't cut your clutch sheaves like the carbon belts do, and you can buy three of them for the price of 1 OEM belt. I've never broken one, I beat on them pretty good in steep tree riding.
It's good to hear from someone running the G belt. They list it for everything up through the 850, so they must think it's up to it; either way, most people we'd consider power users err towards "just give me your strongest belt." I've seen reports of having to adjust the clutching because of losing RPM going to the C12, did you notice that with the G belt? I could buy that it'd be easier on the clutch than the C belt, but I haven't seen any grooving on my primary in the few hundred miles I've put on it. The Polaris belt I was running before (a 3211122), on the other hand, had put a noticeable groove at the base of the primary, which I took care of via IndySpecialties service. I'm still sticking with the C12 unless/until I have a problem, but maybe we are a little too quick to dismiss the G belt.