So does the shorter break-in have anything to do with the compound? I've been very happy with the C12 belts – except for the break-in part, and that's on older sleds with a matching side angle. To properly follow the recommended procedure takes up most of a morning of riding. I've got lucky now and then with enough snow to break one in near where I live, but then I've found having only one correct, broke-in belt means something bad happens to it (my fault, not the belt). So it's hard to predict when you'll need to break one in, and even after a couple full days of riding, the belt still doesn't look fully bedded in.
I thought about trying the 47R belt a couple months ago, but it's much harder to find (talking about the standard 28º), and I figured there'd be little benefit over the C12. But if I get caught out again (though I think I've learned my lesson), I might try the 47R. That said, I had a similar experience to AdrenalineAddict on my last ride: was warm all day, hard to keep the sled cool at times, then finished off the day with a blast back to the truck (fortunately, the snow was more slushy lower down). Other than a small ring at the base of the primary, the sheaves are bright and clean. I also follow something TRS recommended a while back: I grind the side of the top cogs flat (perpandicular to the top of the belt). Seems to result in less build-up during break-in, and probably keeps the belt cooler.