It's true that there is a serious overlay in performance/range between some of the iS and the new Futura and this comparison highlights the importance of understanding the subtle differences in character, tuning and ride style that can seperate or differentiate the two.
If you had a solid 18-20 kts, the ST93 would (by then) be well powered and starting to come well into it's effective (competitive) range, and in that range the gap between both models may not be so obvious. However in lighter wind and also in upwind (or windward) work you will find the ST ultimately not as ruthless as the iSonics.
(this being mostly effected by the bevel on the ST rail vs the tucked but harder iS rail in the mid-fwd section).
Same in the Futura93, which is actually a total new 2008 development board, in rougher choppy conditions the FU93 will be relatively easy to sail fast and "careless" (trim), maintains a super easy and almost auto pilot jibe (you really gotta work to screw it up) whereas the sharper iS86 does deliver better accel and will certainly be at it's best when ridden with a more authoritive (locked) style-still very "free" (and easy over chop) by slalom/race standards - but requiring (and rewarding) that little bit extra technical / active /demanding input to extract(deliver) the real top end.
Short term I think iS86 will be easier to obtain in AUS than the (late delivery) FU93.
Cheers ~ Ian