Andy, just to butt in here with something leftfield... what sort of hillwalking do you do? Day trips outside of winter, snow-free overnight (tent carried) or full winter, multi-day camps?
The reason for asking (because I am also into my hillwalking) is that obviously the pack sizes are vastly different for each of these. I have my summer day pack down to about 4kg including food and water, rising to 8-9kg for an overnight (plus port
), all the way up to 15+kg for a full winter trip (inc crampons, axe etc. but no climbing gear)
Now, trimming 500g off a 4kg pack is not easy - basically involves leaving either layers or food behind (not good!)... but, trimming 500g off a 9kg pack isn't so hard - yes, it might be expensive (ultralight tents can be up to £400) but I reckon I could spend £500 on my overnight gear and bring it down by 1500g or so. Winter packs are a bit more variable according to the type of terrain you're doing, so hard to comment.
So, that's option 1 (non-camera-related) to saving your weight.
Option 2 looks further south. What boots are you wearing? Do you need (and what sort of) crampon compatibility? If you're into full winter climbing then you don't have as many options here, but if it's genuinely just for walking with occasional C1 use, you could easily save 100-125g on boots (and plenty more if you really go for it) by choosing slightly lighter weight footwear options. I didn't and love my trusty Scarpa SL Activs (B1 boots) because of the lack of goretex and overall solidity, but if i wanted easier walking, I would opt for less leather, more synthetics and a far lighter (but still B1 or even B2) boot. Remember that every kg saved on the feet equates to about 4-5kg saving in "pack terms"...
Just a few thoughts, without you having to compromise your camera kit