Just got back in from the afternoon sail on the low tide.
thanks for all the replies. had a much better sail with the flatter conditions

The board was still boardline out of control but i could keep the pressure down through the board because there was a lot less chop. Dropped the boom a bit and down hauled the sail as much as was practical.
I will definitely be looking for smaller kit as we get these fronts here fairly regularly and yes it was 35 to 40 knots as the weather statiuon is only 100m from where I was sailing so you can check the wind speed for every half hour interval.
Will probably look at a 3.5 and something in the 60 to 70 litre range for a board.
Drinking beers tonight and going to the chinese restaurant to put on some weight