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I have a gitzo gt5541ls (the older version of the 4 section tripod). I selected it because I thought it would give a bit more flexibility in packing, due to its shorter length.
I primarily use it to shoot with a 600mm f4 lens on a Wimberley head. It is a great combination. It is more than stable enough, surprisingly light for what it is, and very easy to use.
I seriously considered the 3 section, but am glad I went with the 4 section version.
I also considered the RRS 3 series tripods. At the time they were quite new and about impossible to get. Conversations with RRS at the time revealed they were designed with a maximum of a 500mm lens in mind. Without any compelling evidence they would adequately support a 600mm lens, I decided to go the safe route and get the Gitzo. Since that time, reports from others indicate the RRS 3 series does well with a 600mm lens. You might want to add that one to your considerations as well.
I am completely satisfied with the Gitzo gt5541ls.