A tripod? As in singular? When I retired I bought a D300 to keep my mind active etc. Tripod? Why would I ever need such an awkward device? I took a workshop with Mike Hagan to find out what all those buttons actually did and he had several of his tripods on display and explained why I would need one. I got a Gitzo 3 series with a RRS ball head. Over time I got a 200-400 lens, rented a 600 for a trip to Yellowstone, and started to use 2 TC with a 300 f/2.8. The Gitzo 3 is fine for small to medium lenses for landscapes (HDR) but, for me, using anything over 300mm it is too “light”. I added a RRS TVC-33 with a gimbal to my growing list of gear. A gimbal is a god send, it makes using a long lens so much smoother especially if you are tracking motion e.g. birds in flight. A heavy lens mounted on a track ball wants to flop over thus placing heart in mouth. If you are going to carry it for any distance consider padding the legs to save your shoulder. In Yellowstone I met a fellow photographer using a lens support with a 600mm and he said that it gave him 1-1.5 stops over just a tripod. I don’t know if I get that much but I do get sharper images when I use it. Maybe I’m just getting more skillful? Probably not.
Caution – don’t forget height. If you are on irregular ground, one or two legs will need to be extended to get things level. Add 6 to 8 to the leg length over what your body height demands.
I now have a D800 and the heavier tripod is very welcome. I recently trekked through various estuaries in northern BC to get photos of bears and misty moss using a 28-120 f/4 and my 300mm with and without the 2 TC. In and out of zodiacs was made easier using a monopod. With gear it just never ends. Now about bags . . .