Great article, I'm stoked to check out those trails and taps!
I recently organized a three day bike-packing trip in the rockies with some very steep and prolonged hike-a-bike sections. One of the guys used panniers filled with roughly 30lbs of gear. This made his sub-30 pound bike into a sub-60 pounder and for the tough sections he was hating life (and me). The downhill portions were problematic with panniers as well: bike handling was difficult and jumps were impossible. Based on this, I would say for any trip with real terrain a pack is the only way to go.
That being said, these racks do look good if you want paniers on your mtb.