RE: Which iSonic (94 or 101)
Sorry, quite a few sail sizes/wind conditions mixed in this discussion.
In general, yes the iS101 is a good allround choice for a lighter rider, however that choice would move the sweetspot for that board(sail) combo down the wind range c/w a 95kg rider on the same setup.
(Setting sail size aside - when it's ideal for 95kg on iS101, the 70kg guy is most likely better on iS94 and so on.).
If you clarify your sail range, wind+water conditions/ intended ride style (slalom race/blasting/speed) etc for this board a bit more, we'll be able to provide a more accurate recommendation.
Thanks and Cheers ~ Ian