Here are some tips for sailing fast in high wind and wild water. I am aiming this at freeracers rather than serious slalom guys so if you are into simple blasting with your mates in strong winds - read on.
Your board should be a small fast freeride model such as a Rocket 95 - no more than 58cm wide unless you have the weight and strength to flatten chop (usually over 100kg)
Your fin can be a swept back model such as the Rocket's standard fin but for a bit more speed you need a straight, elliptical fin, raked slightly back (Select S09 for example.)
You need a soft fast sail (Gator, NCX, Cross, Koyote, Revo, Hellcat etc) and you need to downhaul it aggressively. Depending on the sail, a bit of positive outhaul usually improves rig stability as well.
Your lines can be placed slightly further apart than for light wind sailing. Instead of being one handwidth apart, measure from the tip of an outstretched thumb to the outside of the hand for the space between the lines. Lower your boom slightly (not too much or you will be catapulted) and move the mast foot slightly forward. You also need long lines to enable you to get distance from the rig.
You hit the water with your properly rigged equipment, jump aboard and, pulling on the boom with elbows down, hook in and blast off. Your stance is different from the graceful 7 shape described in the piece on light wind sailing. The backside now hangs down a bit and the shoulders are hunched forward to increase the distance of the body from the boom. Your front hand is palm up on the boom.
You need to be extremely sensitive to where you are concentrating your weight. Over easier water you hang more off the boom whereas over rougher patches you will need to stand on the board a little more. This switching of your weight is extremely subtle and requires you to feel and alter the pressure through the harness constantly. You will refine your technique with practice.
Lean and twist forward to power upwind. This keeps the board flat on the water with mast foot pressure and gives control. A useful exercise to develop this skill is to swing right forward while blasting along and try to look around the front of your mast.
Use your front hand to control boom angle. Instead of sheeting in with the back hand, push the front of the boom away with the front hand. Instead of sheeting out with the back hand, pull the front of the boom towards you. This tip is really important when things get wild. You still have both hands firmly on the boom of course but the front hand initiates and controls.
The most important thing if you want to become really fast is to practice, practice, practice. Push the envelope every time you go out in strong wind and try to keep the hammer down for longer and longer stretches. Andy, a local sailor has become one of the fastest sailors in the country in wild conditions and he has achieved this by pushing hard every time he goes out. I remember a session where we were both completely overpowered and seeing him do 3 (maybe 4) frightening wipeouts in one session. I am unfortunately not brave enough to give this level of commitment. Parts of me which get damaged or broken don't heal as quickly as they once did. Andy on the other hand, goes from strength to strength and has started using a very small slalom board in high winds to get even more speed. Bad news for the rest of us.