Opps didn't see your follow-up post. 40-60 litres for the Nahanni IS an ultralight pack, IMHO.

I've got 2 backpacks and 60 litre Osprey pack and a 72 litre MEC pack - for an remote wilderness trip it would definitely be the larger pack for me as it is capable of handling a 50-65 lb load whereas the smaller pack is limited to 45 lb loads. Unfortunately for me, my knees are only rated for 40 lbs!