I also have a Wimberley gimbal-type tripod head for my 400mm f2.8 lens. This head allows the lens to be easily moved up and down and back and forth by providing rotation points at the center of gravity of the lens. Works great for following fast moving objects such as birds. It makes the lens feel weightless yet still provides great stability. The standard head is designed to work with 12lb to 15lb lenses such as the 400 f2.8 and 600 f4. Wimberley also makes a smaller version of the head called the Sidekick which will work with smaller large telephotos such as the 300 f2.8 and 500 f4, although these lenses will also work fine with the standard Wimberley head.
I strongly recommend this head for long telephoto lenses if you want to be able to follow action.
You can order this head directly from Wimberley at their website for $465 without the quick release plate.