I am the same height and just a little heavier than you. In those sort of winds and especially if the water is relatively flat I would be using the higher volume board which would get up on the plane quicker, go through any lulls much better and give plenty of float if the wind died completely. It would also be easy to uphaul if the wind died. I would use 7 and 7.8 camber sails with 44/46 cm slalom fin... I use select S11. At the top end of your wind range the smaller board might be marginally faster but only if the wind is constant.