Probably after mounting, something ard the eye level would be comfortable.
The measurement should not be one where u have to extend the centre column.
You can try to check out max height of Gitzo here : Tripods - Photo | Gitzo The units can be switched btw metric / imperial.
A quick calculation
SYSTEMATIC Series 2 4 section : Height 150 cm
Markins M20 - height ard 10cm
5DMkiii - ard 15cm
Lastly remember to go down the actual shopfront to try out the tripods.
It is really up to you. Ideally I would want a tripod to have a minimum height of 10 cm and a maximum height of 180 cm or so. This is because of instances like ledges where one will be hard pressed to shoot with a wide angle since you would need to bring the ballhead and camera as close to the ledge as possible. Having short legs will result in trouble in that aspect, as I'm sure you can imagine. With longer legs you can well afford to just shorter one and "lean" the tripod forward. There are also situations where you need a taller tripod to "see" over obstacles. With live view, composing without the VF is not so much of a problem.
For the short minimum height, there are times when shooting landscapes when an extremely low angle is preferred.
Of course there are other alternatives to cover this such as horizontal columns, etc, but it really, really depends on your intended use.
Personally I weighed all the considerations and thought that I probably would not need such a short minimum height when travelling. So I stuck to a tripod (non-Gitzo) with a reasonably tall height to allow flexbility at the tall end. And I have another (wooden) tripod for local seascape shooting which is more limited in the max height area, but can go much lower (though still not as low as I'd like sometimes).
Might not be the case. Looking at physics from a secondary/tertiary education perspective, raising the height of the tripod does two things - it raises the center of gravity, and it also widens the base, because of how the tripod is designed. Toppling occurs when the CG goes past the base. So you do raise the chance of toppling when you raise the CG, but at the same time it is reduced when you widen the base. Not sure what the trade-offs would be, but it is not a given that the tripod is less stable at lower heights.
Of course, raising the centre column only raises the CG (all other things being equal at the legs), so this is the only time where it is clear that the tripod stability is affected negatively.