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So then I started looking at the Gitzo gt3542xls and found that the specs fit perfectly for my needs: Somewhat lighter than the 5-series, but still sturdy. Perfect max height 200cm and folded length. The 5 series are either eye level or way too big, there is no alternative in the 170-200cm range.
Given that, as you say, the new Gitzos seem to be better at vibration, confirmed by this test by Neil Rothschild (comparing a 3-series and rrs33, the gitzo wins), perhaps the latest 3-series could suffice? (considering that I shoot at max 200mm).
Would be interested to hear a little more about your experience with the 3-series in the wind.
Does anyone know the leg diameter of the 3- and 5- series respectively? And the RRS-44? Is there a difference in apex size between gitzo 3- and 5- series and RRS?
Also, how does an apex-mounted leveling base affect stability?
The best advice so far is probably from Ellis; so, you might try adding a good amount of weight to the tripod you have, and be sure to have the weight that hangs from the hook on the bottom of the center column actually hits the ground, with the cord very taught. If that improves things for you then the same concept would work if you get a carbon fiber tripod such as the Gitzo or RRS 3 series variants.
When I was using very long lenses with the 3-series carbon tripods, and an Arca Swiss B1 & Z1 heads I felt that the setup was really top heavy, and I had to be careful about not having it too much off kilter on uneven ground, or people (including myself) bumping into it, or the odd strong gust of wind knocking it over, or at least out of placement. Not a major problem, and not a problem at all if you're reasonably careful. However those potential issues are not nearly as much of a problem with a larger pod, but of course those pods are more cumbersome to carry.
If you are dealing with very strong winds, especially unexpected exceptionally strong gusts of wind then you are likely to need the ballast even with the largest carbon fiber tripods, in order to prevent your camera and lens from taking a trip to photo equipment heaven.
I did notice a little wind induced blurring for some telephoto shots with my 3-series carbon tripod that I traced to the legs. However the biggest source of vibration was due to the lens and camera being moved by the wind. If you're using a pano set-up, where there's more surface area exposed to the wind (the head, camera, and large lens) then that's even more of a concern.
You're properly concerned about a large tripod not being that viable for long hikes. The 5-series Gitzo weighs about 6.5lbs, which is really not that heavy, however the larger top plate (which is an important aspect of stability esp. as regards torsion stresses) and the larger diameter legs make it not nearly as comfortable to transport.
When I used to shoot large format cameras (4x5 to 8x10) I found that wind was a real pain - and it was the camera that was being vibrated, not the tripod much if at all. I tried the umbrella approach and one time after a gust of wind blew it inside out and a corner of it into my eye I decided I just didn't want to deal with it any more. Sometimes there just is no 100% solution :-)