Perhaps 1 last remark.
I'm only talking about my own experience.
I find that my IS101 comes close to my son's Fu111 regarding sail size. It's probably the equal OFO tail size between these boards that is responsible for this. The IS101 still feels smaller than the Fu111, but mainly because of its volume and I only feel it when the wind is really marginal for the IS101. What I'm trying to say is that an Isonic of equal volume will feel bigger as a Futura.
So when you want a replacement for your Fu101, I still think it's better to choose a 1 size smaller Isonic. Just my 2 cents.
Mind that there is also the IS90.
IS87 / IS101 / IS122 / US147