I agree that there is such a thing a too small, something the backpacker community seems to eschew [see Tynan article above]. We've been travelling for 6 months

I agree that there is such a thing a too small, something the backpacker community seems to eschew [see Tynan article above]. We've been travelling for 6 months with 40L packs, we're consistently wishing they were about 5-10L larger. However, we make due and are always grateful when we see a fellow backpacker with an enormous bag.