RE: iSonic 101/111 and suitable sail
It's a close call between both the board and sail choice. Compared to the older slalom gear from 80's/90's, the new boards and rigs certainly deliver a much wider, more practical range (sure you're aware), so in some respects (especially for riders experienced with getting the most from slalom/race gear) it pays to be a little "adventurous" (ambitious?) with the expected range from equipment choice /sizing. (looked at the other way, no need to have a different specific board or sail for every 5kt wind range like the old days!). The new boards have comparatively good bottom end range for their size (volume) while maintaining control further up the wind range than wider boards of same width/tail width/sail range..
Based on what you described, the iS101 / CR2 7.7+6.7m would likely be the better choice if you are sailing a lot of (this equipment) at the higher end of 16-25kts, and the conditions in this range are really "solid".
If you're mostly in 15-20kt range, with some potential for 20+ then iS111 with 7.7+6.7m.
If you consider you'll be sailing (or required to be racing) more often in marginal slalom conditions, or the conditions are thin (patchy) for the windspeeds quoted, then the iS111 8.3+6.7m.
(reason here is that with your waveboard to use in hi winds, making use of the new combo to really boost some bottom end range - if you are often in those conditions - makes a lot of sense).
The typical sail range on the iS101 is 5.5 to 8.5m; the sweetspot (on average) is between 6.5 and 7.5m (6.7 and 7.7 in CR).
iS111 typical range is 5.8 to 8.5m (6.1 to 8.3m in CR), sweetspot range around 7.0 to 8.0m.
Of course, these depend on a bunch of variables, including water conditions (choppy vs flat relative to wind range) as well as rider style/preference (some guys preferring a bigger or smaller board for a given sail/wind range).
In all cases, any of the above combos will competitively cover the rider weight/wind range combo, so the decision (differences) really are fine tuning, and you won't be too wrong whichever way you go.
Cheers ~ Ian