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For a 300/400 2.8 you will need the best combo you can afford. Of course Gitzo & RRS come to mind. For the D7K + 17-55 2.8 you probably don't need a $800+ setup and the setup you suggested is excellent for that use, however, a 400 2.8 costs thousands of dollars and it's very heavy so for that I can't see an alternative for investing in an expensive quality setup. I suggest the Gitzo GT2531 with a Markins Q10 or RSS BH-55 ball head.
You can always buy used and save a lot of money.