Just my two cents. I'm using a Feisol 3372 set of legs and a Photoclam Pro Gpld II ballhead with the lever clamp. Shooting with a D 800 and a 200-400 f4 . The ball head is rock steady, easily adjusted and no creeping at all. The legs would seemingly hold any thing you could care to mount on them. They don't seem to have any horizontal torque issues that I can tell and they dampen any vibration in moments. The legs will also fold back over the ballhead for a slightly more compact package though these legs really are quite large and beefy and compact is not an attribute I would willingly ascribe to them.
My previous support system was an old Manfrooto aluminum leg set and Manfrotto ballhead an QR system. this was barely adequate for a shorter focal length set up but not up to the larger lens at all. Needless to say, the new rig is a night and day improvement.
I have used neither a Gitso leg set or a Markins ballhead so no direct comparisons are forthcoming. I can only say that my current set is performing quite well and is a bit cheaper.