If you're still looking at the Crux AK35...
I have an original AK47. It's good, well made, very light and strong, and a typical 'alpine' pack, which I happen to like, but no backpacking bells and whistles (no bladder facilities, very small wand pockets). Mines 45 litres and I've used it for hut-to-hut trips, overnight backpacking, and as a winter daysack. I found that with loads up to around 10kg it's good, it manages 12kg, and much beyond that the harness really struggles to support the load and it gets a bit uncomfortable for prolonged use.
(They may have added a bit more padding on the harness on later models though...)
Edited: 26/04/2007 at 23:36