Neil,
As Gary says above, the Gitzo GT5532LS is ideal. I use my Wimberley Gimbal MkII on it together with a Canon 500 II and its excellent. Yes, expensive but as is said above it really is worth the money. The only other thing I did when I bought mine was to get an extra head mounting plate as I also use an RRS Ballhead and I didn't want the hassle of taking the Wimberley off to mount the BH.
You won't regret it if you go for one.