Right now, in the 2007 range, the iS101 is more aligned as the "100Lt slalom allrounder" (as was S100 ).
This is an interesting discussion, because although the Sonic 100 lost volume to become the Sonic95 (2006) and then some more to eveolve into iS94, almost all the volume (removed) has come from the upper front deck area (iS94 losing just a little more in the rear strap area than S95) ; all of which means in (most, above wind min) circumstances, the S95 and now iS94 aren't sailing a lot "smaller" than the S100 before it.
On the other hand, the iS101 is a particularly verstatile and fast board against the S100/S95/S94, and in test it gets a lot closer to the "smaller" brother than expected ; we really tested a lot with S95 vs iS105 in 2006 and here the results were very close; even on the short rough the iS could be competitive against S95 when iS was sailed with tuning that allowed the rider to keep constantly "ON" the power across chop ; if the sail was lifting (standing up) the rider a lot, the iS was getting a bit more flighty earlier, but if the rig/tuning was open in the head, the power/drive could be kept full on on the iS and it was very fast (against S95) - with the added advantage of better bottom end, increased power handling thru (and out of) jibe and faster recovery to top speed. On super vertical chop (where you are forced to basically "jump" the wave, the tail area of the iS was a bit more of a challenge, but on short to medium, especially stutter chop, the iS101 (105) has a very good flat trim (once familiar with it) that really allows a "power on" style in a more radical way than the (more traditional) S95 /or iS94. The fact you can hammer so hard on the (wider) iS101 really covers the theory disadvantage that it must be "slow".
Antoine has been pretty fast to prove that.
(yes, there is ultimately a rider style/technique influence in this; a more "glide" style guy will probably be more relaxed and confident on the iS94; the one who can "animal" the iS101 without fear will also find great results. No guess which one is A2)
Right now I would probably prefer iS101 + iS87 (iS105+ S85),
but if it was one board only allowed for both those boards range,
well I'd be thinking hard about the iS94 as the one board..
Hopefully you've some chance to demo one of these new options, if iS101/105, take the time to find the tuning and technique to get the most from it; no, it's doesn't take too long, and no, it's not so like HS, but for sure there are a lot of guys with iS101/105 who find even MORE after 2-3 good sessions once they learn to extract the most from the flat trim (and realise they won't die in doing it !
Cheers ~ Ian