So I have resolved that at some point before my planned JOGLE I will lower the gearing.
Current gearing 28/38/48 and 11/34.
https://forum.cyclinguk.org/viewtopic.php?p=1408092#p1408092 has a post saying
How low do your gears go on your bike ??
The lower your gears are, the easier it is to lug the extra few Kgs of camping gear up the last hill before the campsite.
A lot of touring bikes have a first gear around the 25" range for this reason.
Using https://ritzelrechner.de/?GR=DERS&KB=48,52&RZ=13,14,15,16,17,18,19&UF=2150&TF=100&SL=1.7&UN=MPH&DV=gearInches&GR2=DERS&KB2=42,52&RZ2=13,14,15,16,17,19,21&UF2=2150 suitably modified I seem to have a lowest gear of 22.9 gear inches. So already below the suggested 25". Highest is 108".
If I remember correctly, 531colin said that he rode 20/30/40 on the front.
That would give me (with my 11/34 on the back) a range from 101" top to 16.4".
Or a speed (at a cadence of 80) of 3.9 to 24.1 mph bottom to top.
Looking around, https://www.cycletourer.co.uk/cycletouring/gears.shtml suggest that for heavily loaded touring you have a top of 100" and a bottom of 18". So my proposed 20/30/40 is not far off that but slightly lower at the bottom.
So it does look as though changing the front to 20/30/40 would give me a set of gears more suitable for heavy touring (or a flat lander encountering long steep hills).
It does beg the question, though, of how low you can go and still have a rideable bike.
What is the lowest gearing where you could expect to stay on the bike (gyroscopic action of the wheels) when climbing an extreme 1 in 4/25% gradient?
I suspect that the difference between 22.9" and 16.4" isn't going to save me when the going gets tough, but it might get me up some slightly lesser gradients without having to climb off.
I was also advised that dropping the 28 to a 24 (or perhaps even a 22) and leaving the rest alone might be a simpler way to get the lowest gears.
That would give me a lowest gear of 18" or 19.3".
Anyway, I am having trouble visualising how low I should realistically go, and how much difference changes will make.
I could do something extreme like having a largest rear cog of 48 teeth which with a 20 tooth front would give me 13.9" or a speed of 3.31 mph with my legs doing 80 rpm but the changes don't seem massively significant in real world terms.
My aim, obviously, is not to have to replace the rear derailleur and gear cluster plus the front mech and gears because that could be quite expensive.
On the other hand I don't want to make the trip of a lifetime one long misery in the mountains.
I know that "ride more hills" is one answer, but there aren't very many here and certainly no long ones.