> occured to me that the different fuel consumptions measured by Roger and Ryan may differ due to water use, rather than fuel use.
Very possible. Ryan mentioned melting a certain amount of water per day. The amount is more than I ever use per day. But I should add, I seem to use less water than many Australians. I do NOT use a 'hydration system' to drink on the run. I learnt walking back in the days when you drank at breakfast, lunch and dinner, and not in between. Curiously, it never did us any harm, and i come back from trips about the same weight I went. OK, Ryans J's needs may differ.
> Ryan's figures assume producing all his water from snow, and avoiding "cameling up" with 3+L at the traihead.
I would normally set off with one or two 1.25 Litre PET rocket bottles of water. But that is for myself and my wife. In this case, I might take 2 bottles with me at the start.
> He also boils his water to prevent freezing, and to augment the warmth of his sleep system.
No, I do not do this. I get the water to about body temp and leave it at that. If I want to put some in the SB overnight, that is an OK temp as long as it is insulated from the snow. It does not drain heat from me if it is at the same temp.
> Roger seems to rely partially on finding liquid water,
True, and really worth while. Can Ryan J do this where he is going? I don't know.
> cameling up,
Not really: I just drink less. I don't mind a slightly dry mouth - it never hurt anyone. Teaches you to keep your mouth shut too! The Bedouin do this in the desert.
> and perhaps merely melting rather than boiling the water.
I can't see any need to boil water from snow????
Some else asked about sleep systems. I assume this is a fancy name (you Americans!) for a sleeping bag and a mat? I use 700 g 700 loft SB as a quilt, but I have to admit I also use a Therm-a-Rest Deluxe airmat under it. At 60 years of age, I reckon I am entitled to it!
I wear thermals if it is cold, or light silk pyjamas or a silk liner anyhow. The SB has a hood - I would NOT buy one without a hood!, and this goes over my head when I am sleeping. A warm head makes for warm toes. All those ads for extra down at the feet are marketing crap. These days I sometimes take a light 200 polarfleece ski hat to bed when it's really cold too, and maybe a dry pair of socks to pad my toes off the deck.
The coldest night I have used this gear at was -17 C (1.4 F), but I only had the thermals on - no extra clothing. The night was OK, but the wet ski boots in the morning were ... :-) I think we wimped out that morning and warmed up the milk for the muesli.