Some unanticipated events have caused me to tighten down on my gear budget for next year so I'm sticking with what I've got - and luckily the Circuit is a great pack based on my experience on the JMT this year and I think it should serve me well on the Colorado Trail. I am planning on a PCT thru hike in 2015 - maybe I'll reconsider the Arc Blast at that point, or maybe just stick with the Circuit. The Arc Blast does look like a sweet pack in terms of weight and from the videos I've seen it looks quite large as well. I'd love to see one in person at some point.