Another late-to-the-game post, but I think when considering a ballhead to use with a heavy lens, the Acratech GV2 should be at least a consideration. With 300/2.8 class lenses and longer, it's extremely convenient to use the ballhead in "faux gimbal" mode, by dropping the ball's shaft into the head's portrait groove so you only have to deal with vertical movement with ball rotation, and horizontal movement with the panning base, this eliminating camera tilt as a consideration when shooting. This mimics the action of a gimbal head, and if you also balance the camera/lens on the head with a long lens plate, handling the big lens is very easy. You can, of course do this with any quality ballhead, but the Acratech GV2 and GP series heads have a bearing sleeve around the ball's shaft, and a reinforcing pin at the bottom of the ball, so you have only two bearing surfaces, instead of the ball surface bearing against the top of the ball housing for vertical movement, and the ball's shaft rubbing against the portrait groove. One caveat to using a head like this is that it will unbalance your tripod setup, and if you're using a relatively narrow leg angle, with a heavy lens, the whole thing can tip easily if you leave it unattended (you need to get into the habit of centering the camera directly over a leg if you walk away, even momentarily). Also, with less expensive heads, you may find that the panning action is not very smooth as the offset weight will not be handled well by the panning base, or the panning friction cannot be set precisely since primitive screw locks can actually damage the bearing surface.
The GV2 or GPs are pricey, but worth it, IMO if you're going to shoot the big glass a lot. At the very least, I'd consider a long plate to balance the camera/lens on the ballhead, even if used as a normal ballhead. It will make shooting the big lens a lot easier since you won't be fighting the lens' weight as much.
Relatively inexpensive long Arca type plates can be found on Ebay from rainbowimaging. They are a good US seller, ship quickly, and the plates are of good quality.
Here's a link to one of the longer plates, a 150mm :
Lens Plate Quick Release Arca-Swiss Nikon 200-400MM VR | eBay
@ $25.99 it's close to half of what you'd pay from Acratech, Wimberley, or Kirk. They also offer both longer and shorter lengths
Scott