Sorry Giu, I'd like to respectfully disagree on 3 counts but agree on 1 with you :
1) There is way too much overlap between a 110 2013, a 117 wide 2012 and a 127 2011 iSonic for a very light weight 62 kg rider;
2) His 8.7 and 9.3 sails are badly matched to his 3 board quiver as depicted above for a 62 kg rider.
3) Didn't try a Z-fin, so I cannot comment on that. However, a R16 46 or 48 cm fin is too small on iSonic 127 with a 9.5 sail for light wind sailing whereas a 52 cm is just fine. The 48 cm fin is fine with a 9.5 sail but on an iSonic 117 Wide, however.
Agree with you on 1 count:
4) The difference of low wind range between an 8.6 sail and a 9.5 sail is very small : 1 knot earlier planing with the 9.5 sail for myself.
If he gets a much larger sail like me, then the difference in low wind range will be much more significant : 7 knots planing with a 11 m2 sail versus 10 knot planing with an 8.6 sail. In 3 Bft wind, 3 knots is a huge margin between planing or schlogging. With the very same 11.0 sail and 55 cm fin, I've found no difference in starting & sustaining the planing with either the iSonic 117 Wide or the iSonic 127 : both do that as of 7 knots of wind. In fact, I do like better the 117 Wide because of her way smaller footprint underfoot. The iSonic 127 did feel like a big tanker: didn't like it at all and was pretty much disappointed to say the least IMHO.
In sum for my 65 kg weight, the iSonic 127 is useless because her wind range is way narrower than that of iSonic 117 Wide. For your heavy weight (i.e., 90+ kg I guess ?), this is of course a much different story...
Cheers !
JM