RE: iSonic 87, 94 or 101
Considering, for this discussion that your range is spread across 15-25kts, (not 80% 25kts with only a few rare days below solid 20), then the 101 goes along way (more than the 105) into "traditional" 95 territory. Maybe also a lot of riders are getting used to the iS style, more familiar with the ride, and how to get the most from it - which is a slightly different style to the traditional. Most of us have a very positive rating for the "old" 95 - and we know from testing the new 94 actually tops it (95) by a narrow but noticeable margin. So it's no lemon.
If you had only one board to cover the 101-87 range, logically the 94 remains a very good choice as it really carries over some of the traditional "hi wind" ride/feel/handling, and it also is very competive with 6.6-7.6m conditions for your size. However for 2007 range, the 101 really extends so well into "95" territory (in most locations/conditions) that it becomes a pretty compelling choice when considered for your size in the 7.6/6.6m + 15-25kt range.
Obviously, the "advantage" to the 101 is seen more at the lower-mid end of the range, or in gusty or patchy conditions. While it flies off the wind, the iS style (101/105) has an advantage in "upwind" slalom angles as well over narrower slaloms.
Considering your strong feelings towards a more "traditional" slalom (S95 etc), the best suggestion is to try a demo ride on a 101 if at all possible. By all means try a 105, but the ride on the 101 is even more "95" than 105 (101=better hi speed trim across chop/ better jibe) - so be aware if you test 105.
It's only a calculated guess, but I think if you (only) try 105, you might VERY narrowly stay with 95 or 94, but if you try 101, then you would see enough potential that it would become your new choice. Not so much because 101 is a better board than 94, but because 101 fits and performs so well in the wind/sail/quiver range you discuss.
Cheers ~ Ian