Notwithstanding the heretical nature of you even having posted photos of an external frame pack, let me congratulate you on the finished prototype you posted photos of. It looks great, it looks light and it looks comfortable! I love the ess-bend frame design on the K2, also.
Out of nostalgia and frugality, I use an external frame pack with the lightest loads I can manage inside it. Mine's a 1980 Kelty Tioga XL with 2009 shoulder straps but the original cam-lok hip belt. I have owned and used internal-frame packs, but they were heavier than the Kelty and were not as comfortable. I enjoy the ventilation, the ease of loading, the organization of my external pockets and, frankly, the ability to carry loads such as a large bear canister inside the pack without sacrificing stability or security of the load. I even keep the removable extender bar in the pack, because there have been those times where it's been useful to strap on either deer meat or another hiker's pack...and I am nostalgic. :) Total carry weight for 7 days, including 3 liters of water, full BearVault 500, stove, fuel, all of a tent, REI tripod stool, kite, camera and "croc-off" camp shoes is reliably at 35lb on day one and the rig carries it "lightly" if that term can apply.
Having carried 62lb in the same pack, I can assure you, 35lb can be lightly and 27lb for a summer weekend is heavenly.
I think the K-2 system needs a pack cover to protect the upper load from sun and brush.