I am thinking of getting some long(-er) glass. The big whites (and blacks) --- 500mm f/4, 300 f/2.8 etc., 400 f/2.8 etc. --- are out of my price range. I am trying to decide between the EF 400mm f/5.6 or the Tamron 150-600mm or the newly-announced Sigma 150-600mm. I am using a 6D.
The longest lens I have got now is the EF 70-200 f/4L IS, and most of my images are landscapes and/or macro (with the TS-E 24mm or the Zeiss 21mm, and the EF 100mm micro, respectively). Hoping to start getting some of the larger or more approachable wildlife, such as bigger water birds or mammals. I am one of those who find that I like longer focal-length landscapes as well, but that will be secondary application.
Currently my support is a Gitzo Explorer GT3541 + RR BH40 ballhead.
How do folks with experiences with these lenses or comparable ones think that this support will hold up for the lenses I am considering?
Will a monopod + monopod head hold up? Or would I need to go the full 3-series or 4-series (or equivalent) + gimbal route?
Thanks for any advice or suggestions or feedback.

