RE: Changing F Type 158
It's an interesting perspective you put on the new boards.
The historuy of the larger FT's is that 1)mostly the guys owning/riding them did not take the sail size out to the limit and 2) did not really spend a lot of time sailing full upwind/downwind (FW style) , rather they used them for cruising and light wind back and forth (in this mode, the iS155 offers a very good package, a little more atuned to those "average" user needs/wants).
Agree that in your specific case, for 100kg the iS155 is not so ideal with 12m, and likewise even with 100kg the Apollo is basically a board for up to 15 kts, by 20 it is pretty much done and certainly the F161 becomes a more competitive choice - and an easier ride.
Agree that a Formula won't jibe as well as the iS155 (size for size), but by perspective the FT158 was not really a jibe machine either, coming closer to F161 than iS155.
It's indeed a difficult choice, and sorry that the the overall improvements (and customer/dealer/market fed rationalisation/s) to the new range have left you a little compromised.
Please let us know if you would like more info etc.
Cheers ~ Ian