For 2007 iS with 80kg "typical" rider :
iS101 : 7.0m sweetspot
iS111 : 7.5m sweetspot
iS122 : 8.0m sweetspot
iS133 : 8.5m sweetspot
Obviously anything within +/- 0.5 m of above will still be well inside "ideal" range.
Personal style (and local water state conditions for a given windspeed) still play a noticeable role, some riders prefer (for a given wind - or sail - range) a slightly (ie : one size ) bigger board tuning and "blast across the top" (of chop) type style, whilst others prefer the smaller, more direct and calmer type ride (board sits down in chop) of the smaller board option for same conditions.
Me personally (92kg) would have no hesitation to take 101 for 7.3m if it wsn't marginal 7.3m - and especially if I wanted to have good 6m range in this same board as well. Despite the volume the 101 sizes very "101" when it's being sailed, and although some compromise could be argued in static uphaul mode, it's not often an issue..
However, (as the small variance in sweetspot confirms), the 111 is not out of the 7.3m frame at all, and tuned/sailed in the "blast across the top" mode in more powered / choppy conditions has been shown to be an effective (competitive) on-water option to the 101 while still retaining some extra "reserve" of volume and planing threshold. (everything else being equal, which it rarely is..). One significant variable is how "performance" is judged; ie : in short course slalom racing , acceleration (ie ;bigger board) can also be more effective than a marginal difference in top end speed. Conversely, in open water/ long distance (or pure "top end drags/blasting with mates) accel is a less issue than top speed. And please note, the full "blast across top mode" is usually more committed, more challenging - and less comfortable.
It's not for everyone. But it's also not ineffective ..
So all jokes aside, I'm not dodging the (marginal) question.
I'm showing you how to (best) resolve it for yourself !
Cheers ~ Ian