In reply to kwoods:
Just because it feels/looks like your core goes, don't assume it necessarily is. If you're on better holds, you've got more in hand to allow you to manoeuvre body position and still hang the holds. If you're tired on the holds and they're closer to your limit you'll find it harder to do core intensive moves, even if your core's not tired. In the same way that you can hang holds at your limit but not necessarily move off them, but that doesn't mean that your arms are the limiting factor.