I spoke at length w/ a guy who did surf photography for a living at one point (I bought an EOS-3 from him, as well). He told me that he pretty much exclusively used the 600/4 on that camera (full frame 35mm). The equivalent of that for a 1.3x crop factor body would be a 460mm lens (so, either a 400mm or a 500mm), and for a 1.6x crop factor body, a 375mm lens (so, a 400mm).
The 1DMkII(n) is a nice camera, for sure - I wonder if a 20D/30D might get the job done for you, and free up the cash for the glass you need (at least, to get you started)?? That gives you more options to get out there....
I don't have any experience w/ the 100-400+TC combo - seems like it might end up awful slow on the focus side of things for surf (they can cut and move pretty quickly, and you don't often have a lot of time to get on a surfer, get focused, and snap frames)...
?