So I've bought a 20yr old 150 litre formula racing board Kinetic Centurion 2 designed by robbie radis.

Im kind of a beginner but I want to go fast. I'm 110kg. What size sails do I need to get me and this board screaming across the water? I currently have a 5.5 but I think it's too small. Looking to sail in average winds in Perth.

Perth based. Thanks guys