To get back on topic, however amusing the diversion might be <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Are you able to flatten your mainsail properly? If you on a quiet day sheet the main as hard as you can and apply max downhaul, does the main go completely flat except for the lower third? When the wind really pipes up, it is important to be able to trim your sails flat. On our boat we aim for a really flat sail when applying max downhaul and mainsheet.

When sailing in high winds, I dont think you should aim to trim the downhaul all the time. Set it so you are fully powered up in the lulls, and use the sheet to depower a bit in the puffs. Crew handles the sail controls and spots gusts while helm is sailing the boat, no more. Also, realise that by dumping the main you let the mast straighten, especially the upper part. A straighter mast makes your mainsail fuller and let the jibs luff fall off, this power up the boat instead of depowering. If you are easing more then 30-40cm of mainsheet in the gusts, I think you should either use more downhaul, or if maxed out let the traveller out a bit.
It's amazing what windspeed you can go fast in when you get used to it and adapt to it step by step. It is partly about skill but mostly preparing mentally. It can be hard on the gear tough!