Update for anyone finding this later: it was the pad and the neck gap together. New pad plus a buff and I slept through at 36F last weekend.
Checked on the next trip and my hip was cold against the pad, so it is partly that. R4.5 is the manufacturer number and mine is three seasons old.
Running fitness transfers less than you would hope. Walking uphill under 14kg for eight hours uses your hips, calves and lower back in a way a 40 minute run does not touch. If you want to shortcut the adaptation, do some loaded walks at home — an hour with a full pack twice a week for a month makes the first days noticeably better.
Half a size up may be too much if you are also running two socks. The rule of thumb is a thumb width in front of the longest toe, with your normal hiking sock on, laced, standing. Some people need a full size, some need none at all.
It is the most useful thing in this hobby that nobody tells beginners. Works for downhill toe bang too.
It did say exactly that and I had read it three times without understanding what it meant. Obvious in hindsight.
Zone c had exactly two nodes and I drained one of them, the other was full. Added capacity in that zone and it bound within seconds.
60 litres is very low for a hollow fibre cartridge, so something in your water was dirtier than it looked. Clear mountain water still carries fine glacial silt and organics you cannot see. Pre-filter everything through a bandana or a coffee filter into the dirty bag — costs nothing and multiplies cartridge life several times over.
Hybrid, weighted by town size. Post boxes only to the two small towns where the single shop might not have what you need, and buy in the three larger ones.
The budget angle usually favours buying as you go, because posting adds real cost per box and you buy in bulk at home which then sits in a box for three weeks. But the failure mode of buying is arriving at a village shop with three shelves and a dietary constraint, which is a genuinely bad day.
Being tied to opening hours is the thing people underestimate. Check whether each collection point holds parcels at weekends before you commit, because a box you cannot collect until Monday morning costs you a day.