RE: Fins/Sails S-Type 93
You're on the right track taking a more cammed sail for the larger (ST93) sail sizes and then complimenting the rough water speed aspect of the 93 with more "control" sails in higher wind /rougher water.
Expect the ST93 will sweetspot around 5.8m, but you may (or not) prefer a slightly free/er sail in that size, rather than a fully locked racesail (X15) for Perth 5.8 conditions.
Unless you're a fully dedicated, no compromise boy racer, you might find a higher s/miles per hour ratio on a good (draft stable) fast freeride sail (few cams, or even nocam like Severne NCX 6.0) in the larger sail range as well. I've also had really good ST 93 results using Severne S2 (fast freemove) in both 5.8m and 6.4m(about the upper practical limit for my weight on 93)
Stock 34 fin will be OK for around 6m conditions, fully powered 6m something around 30-32cm will also double as good choice for higher winds (technical catch here is that these sizes relate to fins of similar aspect ratio to the stock one (moderately hi) : ST93 can be tuned very nicely - especially for rougher conditions- on lower aspect ratio fins as well, which yields a lower "size" (depth) , but a similar performance size recommendation....That's to say, a moderate lo A/R 28-29 would be same perf size as a higher A/R 32 (make sense?) . All of which means you got a lot of choice and range in the fin side of things.
Cheers ~ Ian