Thanks.. Well the iS122 seems like a good bet too. My 8.5 is a Tushingham T-Bird, no-cam seven batten low footed freeride sail. It's actually quite fast and it has a very huge range. No problem sailing it in freerace mode (I've done 32 knots on my ST115 with a T-Bird 6.5 once) but of course it wouldn't win a world cup (I don't compete unless someone tries to overtake me;-).
The iS122/8.5 I guess would work well into the ST115 (or Aero with 6.5) range. That would give me a lot of choices in the middle wind range.
I don't know if the F133 is too much of a compromise. I guess the iS122 planes earlier and goes faster...