A big G1504 Tele Gitzo Studex "Giant"(4 extension sections per leg) will probably do the trick. One of the tall, aluminum ones. Might seem like overkill, but they're heavy, they can go really tall(like 8+ ft w/ the center column cranked up), and with a No5 3-way head, proves to be a very solid combo.
Ries is also another great option, but you'll need to add leg extensions to the base tripod if you intend to go up in height. The studex giant has it all built-in, albeit at a cost of extra weight.
Even with the GX680's excellent mirror-dampening, I've found that using mirror-up still gives the best results, when possible. Less mass moving around makes sharper pictures
-Dan
p.s. Watch ebay for the big Gitzo's. I got mine there, and despite not needing the height capabilities of it much(if ever), I still regret having sold it a few years back... They're cheap as chips(almost) these days, I think I paid ~$350 shipped for mine, with the #5 head(which I still own and use on a CF Gitzo now)