The majority of what I shoot is watersports, and I use a 7D and a 70-200 with a 1.4 converter. It is an excellent body for this use. Good sealing, light, excellent AF and the high resolution sensor leaves lots of scope for cropping. It has all the custom functions you need to set it up for this kind of sports, which the 30/40/50 range lack. The defaults seem to be more focussed at shooing field sports, and do need some adjustment for watersports.
Lens wise I find the 200+1.4 comb is fine. It give a 450 effective length on the 7D. Hand holding anything longer is a bit tricky!
The choice is really down to whether you are going to be on the water shooting or on shore. If you're afloat you need a weather sealed lens that's light and compact enough to handle in a boat, and it's going to be a small boat if you're shooting surf. Anything longer than 450 equivalent is going to be impossible to hold steady in an open boat. In fact, once it gets at all rough I always end up taking the 1.4 off, since I can't track anything at 450mm in a pitching boat anyway.
If you're on the beach you need to go for a bigger lens and a monopod, but you won't have boat motion to contend with so you should be able to use whatever focal length you can afford! The disadvantage of this is unless you have serious £ to spend you aren't going to be able to get the same big aperture and fast shutter speeds.
