So as the OP, i think i've now narrowed down my choice to a couple of options, being either the RRS TFC-24L or TFC-34L.
This is mainly because
(i) both extend to the height that I'm seeking, being c 170cm high with no center column, and
(ii) both are pretty narrow in terms of packed diameter due to the Fixed Apex "TFC" design (more so than the RRS Versa "TVCs" or Gitzo Systematics which have bigger head plates), which might help keep it compact on a backpack for hiking.
On paper, the differences seem not massive between the TFC-24L and TFC-34L, ie, respectively their folded length is 59cm and 61cm (so very similar), their max height is 168cm and 174cm (again, very similar), and load capacity is 32kg and 36kg. Both are presumably ample in terms of load capacity for my GFX100S and max 80mm lens, and certainly a lot lot more suitable for my needs than my current Gitzo 1 Series Mountaineer that's short without the center column and weighs less than only 1.3kg! The weights of these RRS models are roughly 1.67kg and 2.1kg, respectively, so some difference between them that might be more noticeable when carrying up the mountains.
So my question is whether anyone has practical experience of both the 2 and 3 Series tripods from RRS ....do you find there to be much difference in stability owing to the different width of leg tubes and different weights .....does the RRS 3 Series feel noticeably "bulkier" in use versus the RRS 2 Series ...and is this difference likely worth it for a 100mp camera that i'd often use for landscapes?
Many thanks for your help.