My experiences may help you with this issue. We have been struggling for height and speed and generally we where over powered in anything over 10 knts. After much testing and advice, in 15 - 20 knts of constant sea breeze here are the settings that worked for us:
1. Mast Rake - Side - 2nd from Bottom - top 2nd Hole down - very tight rig
2. Spreader depth 80mm (approx 3 inches)
3. Pre-Bend - approx 45mm (approx 1 3/4 inches (did say 2 3/4 - wrong conversion
4. Rotater - (this will cause a bit of a stir) well forward of the stay and in fact its now always set to that. The leech of the jib just misses the spreader arm (on the beat). We now never touch the rotater, up or down wind.
5. Cunningham - on as HARD
as humanly possible even harder than that!
6. Mainsheet - pull on to the max
- your crew should only need to let off 6 to 9 inches of sheet - and you can head up slightly in very strong lifting gusts. In fact the main is so light you can hold it with ease, so when the crew has to pull on a heap more cunningham he can hand it to the skipper and its not going to pull out of your hand.
7. Hard battens in the top two - all battens just snug - not shoved in hard - just take out the wrinkles
On an STX this will invert the main on the beach and be dead flat and on the water the top twists off just like the Tiger on the far right hand side of the photo you included in this post. Its un-believeable - totally transforms the Tiger into an absolute weapon in 15kts plus
The only other point is I am running 10:1 on the main (As I am old and daughter is crewing for me) - we are using the new Nacra 5 sheave Harken top block - down to the usual triple and a double on the top of the triple.
If you get one I can help with the sheet threading as it is a bit different.