My two pence on what would be good for shooting surfing. Firstly it is going to depend on how far away the break is from your vantage point and how much spare cash you have kicking around.
This summer I should be shooting quite a bit of kite surfing so for this I will be using the Sigma 300-800mm f5.6 (Sigmonster) which will give the flexibility needed for the events. Options I think you should look at include this baby but also the Canon 300mm f2.8 which is renound as the sharpest lens out there so good that you will get fantastic results even with the 2x telecon so if you went with that and a 1.4 and 2x you would have options of 300mm f2.8, 420mm f4 and 600mm f5.6 lenses so there is flexibility there. I have recently been shooting with the Canon 100-400mm f4.5-5.6 L which if you get a good copy will give nice results (I have posted a couple below). This is a good compromise lens as it is not too expensive and has good range and quite fast AF. If you are looking for a longer lens then the 500mm f4 L is nice and I would personally choose this over the 600mm as it is light enough to hand hold (if you are reasonaly strong) for shots(ish) periods of time and again will work great with a 1.4x telecon. Last option is going back to Sigam and the 120-300mm f2.8 which works well with the 1.4x telecon and still gives usable results with the 2x.
More food for thought LOL.
He does not like me showing this one but this is what happens when you land without a board !!