Hi Jet, welcome to the Cameralabs forums!
I quite fancied doing a bit of skateboarding photography myself, and have dabbled at the sides of rails as snowboarders have whizzed past - see http://www.cameralabs.com/reviews/Canon ... age5.shtml
All the pro photographers I've spotted at these events seem to rely on multiple flash guns, some mounted on the end of monopods held high over their heads... They also use wide angle lenses and get very close to the action, often also liasing with the boarders to find out where they (hope) to go.
So from my limited experience, it sounds like you're already getting all the right kit, so it could just be a case of finding the right spots and taking lots of shots. I'm sure you're already doing this, but you should also check out the kit which other serious board photographers are using at parks and asking if they're happy with their setup, although again your list looks pretty much like what I've seen being used. Does anyone else have any suggestions or tips? Let us know how you get on!