RE: For Ian Fox: ISonic 111 vs 122
For 100kg+ riders in the 15-20kt range iS122 should be the magic size;
The "big" (pun intended) advantage is the ability of the iS122 to just blaze across the top of moderate chop (with the right rider attitude/familiarity) and in this mode the 122 is certainly not slow.
If you were going to push for pure speed and were constantly in solid 20(or 20+) kts then yes for sure the 111 comes into the frame and potentially could deliver a marginally faster top end in these (powered) conditions, however in anything less, the 122 will be easier and potentially even more competitive. One thing that I have noted is how (relatively) high (like well into 101 territory) a heavy, blasting rider can go on the 122. As the water becomes choppier, the 122 carries the extra width very well and has a very effective "tail ride" stance blazing across the top of chop, compared to the deeper, more "rail engaged" ride of smaller narrower sizes (which are certainly calmer but also require more careful control/trim in these conditions).
Early planing and ability to handle bigger fins (comfortably at speed, not just sub planing) is again a very real advantage to larger riders using 122 (bigger, stronger, heavier riders have the advantage of being able to take (and use) the extra (tail/fin) lift that would start to become uncomfortable for lighter riders in the same conditions.
(122's no FW either, so be aware with 100+kg on top, it won't plane you off like one either, esp with 7m ...Unless you're really getting solid 20 kt wind a lot, boosting the sail up to 7.6/8m with an effective variable outhaul is definitely another very real 15-20kt potential; 122 likes and takes a fairly "overpower" trim very well indeed.)
Jibe on the 122 is again rather special (One of it's real plus points - for a 120Lt slalom - in my book) and again with a small amount of experience(familiarity) you'll be able to stomp some jibes that would please a 100Lt freeride rider..
Understanding your comment about the general preference for smaller boards, but especially with 104kgs to make use of, certainly no need to fear the 122 being too big in your described range.
Please let us know if you'd like more info/discussion etc.
Cheers ~ Ian