RE: S-Type 93 2006
With your weight the 28 will work very well with your 5 & 6m sails. Having said that a good 32cm slalom fin will help with early planing, reaching speed and pointing with you 6m sail, especially in the lower/mid end range of the sail, say 15-20 knots. I almost always use a 34cm slalom fin with a 6.5/79kg. I mostly use 2 fins for most sail sizes. this extends the range of the sail, without having to rig down. Its far easier to change a fin than rig up a new sail.