RE: IS87 or ST93???
Both boards offer very good hi wind RS 5.2m blasting solutions, and you shouldn't fear the iS87 thru chop too much ; in fact one of the most noteable comments from (non owner) users is how "magic carpet" the iS87 is across chop for a full on slalom board. However, this board still rewards input with performance, and as such it benefits from being ridden in a more concentrated, technical manner than the ST93, which has a very easy ability to blast over/thru chop at high speeds without the same attention to rider input/detail.
If you're really serious about hi wind performance or racing and also want the best possible "light wind" performance (...range) from your hi wind board, then think more towards iS87*. If you're more into hi wind blasting for casual fun and/or enjoy the less "technical" ride in these conditions, and if you want a little more "bump and blast" capability, then think more towards the ST93.
* Please note that 7.2RS Racing will be bigger than ideal for both these boards (and so impacting on your "light wind" use of the hi wind board). Both boards will carry the RS-7.2 but the iS87 will actually be a better match in these conditions.
Chers ~ Ian