That's a beautiful thought: those myriads of people I passed on my brief intersection with the Routeburn with their tiny 50l packs were labelling me as a novice tramper as I disappeared off into the distance with my full 80l pack. Good for them!
Amusement aside, you've summed it up nicely. It's down to what you want from a tramp. The sacrifice of leaving anything I currently carry behind would be far worse than the weight penalty of carrying it. I could invest money in lighter, more compact, more modern gear and certainly get down to 60l ... will indeed do so as things need replacing. But to be honest, so long as I keep using it, the weight doesn't seem to affect the distance I can cover in a day. Suspect a smaller pack might hook up less on supplejack & the like ... now that would be a real bonus.
But that's me. Your experience will vary.
it's easy to suggest people lighten up with their gear, but light gear is often more expensive, sometimes a lot more expensive and not everyone has the money to spare to do it, depends what your priorities are...
Waynowski said it right. Depends on the tramper, the trip and the experience they want. There is no "right size". Although there is a wrong size - one that you can't carry, or one that doesn't have room for the necessary gear to keep safe. Last trip we had to fit in three stuffed seals, or the kids would have screamed all night :-)
For years i stayed at the cutting edge of gear and equipment. Ultimately everything is a trade off between durability, weight, cost and usefulness etc.
Speaking from experience, i would prefer a bigger pack if i'm restricted to one pack to do everything, because the harness will offer the best support regardless of the weight.
There's one thing i know for sure. Carrying a little extra weight and getting in condition for it can only make you stronger.
We are all different and i know on many an occasion i have been perceived by others as something or other in the way of a tramper. I've made habit of ignoring it now. No-one knows where your going half the time, or where you've come from and for how long. They don't know you or your experience.
One aspect of carrying a light pack means you'll get there sooner which could be useful safety-wise and also you may be less likely to injure yourself whether it's preventing a slip or hitting the deck with less impact. I travel with someone who often has a pack twice the weight of mine and the bigger they are, sometimes the harder they fall.
I'm at the age now where I'm hoping to minimise wear and tear on my aging joints, ligaments and tendons which are slower to heal at my vintage. Carrying a lighter pack helps me in this regard. My 64 year old brother goes very light and tramps with younger and pretty speedy companions, doing some amazing trips.
Good point @aardvark. As someone with lower back issues I've found that tramping with my 80l pack keeping my back in line no matter what I do is a great cure for a strained back.
Whereas the 45l daypacks / trapping packs we have at work are a very effective cause of backache - no lumbar support and transfer a lot of pressure into the small of your back.
A good harness is worth a lot.
I still have a Mont mountain guide 90lt pack that is serviceable. I haven't used it in a long time. The pack weighs less than many day packs 1.9kg.
It was designed as a throwaway. It actually retailed 10% higher than the canvas equivalent. The fabric is a light ripstop polyester. It is assumed a guide would use it alot in a short time and the sort of loads you can get into a 90lt would sooner than later tear the fabric. I recall getting close to 38kg in it once for 9 - 10 days out. Ropes for glacier travel included. The harness is very supportive.
The upside was that i got the pack new, free of charge, to use for twelve months and thrash it a bit. I wrote a report and sent it back to Mont. They reinforced the worn parts and sent it back to me to keep.
I do recall in my very early days, ignorant and stubborn, i put two days gear etc in a 30lt. It was like a ball on my back. It resulted in all the weight on my shoulders. In a pack over 40lt i believe you should seek a hip belt that will allow you to transfer 75 -80 % of the weight to your hips. Legs muscles are bigger.
Any pack over 50lt or more will do. If your worrying about things like packs and jackets for a tramp like the routeburn you might be in the wrong game. Just throw a jacket sleeping bag food utensils etc in a pack and hit the trail. Old new heavy light it shouldn't matter. It's full of people. It's easy. It's short. Just do it.