I use both a tripod and a monopod, as needed...
My "field" tripod is an older carbon fiber Gitzo "System 3" G1325.... no center column. Gitzo levelling base for quick setup. Kirk BH-1 ballhead. Usually with the big lenses I use Wimberley Sidekick gimbal mount that works in conjunctioin with the ballhead. I have Arca-Swiss style plate on the lens, that matches up with A-S platforms on the ballhead or the Sidekick.
Never had any problem with it in ten years or so using this rig. It's plenty heavy enough to accomodate the 500/4 IS, also a 300/2.8 IS which I use and certainly some lighter lenses... I don't have, but might not be as comfortable using it with the original 400/2.8 or 600/4 non-IS or IS, all four of which are pretty hefty lenses (I know people who use similar rigs, though, with various of those lenses)... But it certainly would handle the Mark II versions of either of those lenses and would be fine with the 800/5.6 IS.
I prefer the Sidekick over a full gimbal head, because it leaves the tripod and ballhead alone, so it can quickly be converted back for standard use. (King Cobra, Jobu, etc. convert the tripod and make it pretty much "big lens only", unless you swap out the head.) Also, the Sidekick works well to mount a camera vertically, when using shorter lenses.... So there is no need for an L-plate on any of my cameras, just a standard Arca-Swiss plate.
I never carry the rig very far over my shoulder... that's just asking for trouble, no matter how heavy duty the tripod rig. Short distances... yes.... with care.
I have two Bogen/Manfrotto metal monopods. One is simjply modified with an Arca-Swiss style QR platform on top. The other has a medium size Manfrotto ballhead that's been modified with an A-S QR platform.
It depends upon what you shoot.... whether you need a gimbal or not. I certainly do... shooting sports/action, wildlife, birds. A gimbal such as the Sidekick or one of the "full" gimbal heads makes it a lot of fun to use the big lens.