The only reason for switching to the RRS was height. I never had any stability issues with the Gitzo. But the RRS gives the same height with only three sections and it has beefier legs. The head base of the Gitzo is slightly wider than RRS. The RRS is slightly longer, when collapsed. They can use the same base plates, level bases etc. Because of the wider head base on the Gitzo, it is marginally more cumbersome in transport.
You can live happily with both. But make sure you get a good leveling base.
The reasons why you choose RRS are the same as for me.
I think I will go with the RRS leveling base with hook. I know it will stop the tripod from getting as low as without the hook but I normally know when I leave home what I´m going to photograph. So if I want to have it very low for macro I will leave the the Gimbal head, leveling base and so on and have another plate for my ballhead for the macro lens instead.
Be aware that the Gitzo has a much more convenient base place release mechanism. With the RRS you need tools, whereas the Gitzo can be done without tools. According to Neuro you can buy both the handles for the leveling base ($35 each I believe). I have the short one, without hook, but will buy the longer with hook.