Not the team here, but I know that Remi & co do not use Select fins. So may not give you your answer.
I am a bit heavier than you (98kg/194cm) and have the iS137. The iS127 is flat vee to mono concave and the iS137 is flat vee to flat but they both similar fin requirements. It is quit hard to tell/feel the difference between these two boards in light winds.
I mainly use a 9m on this board. Some times a 8m and 10m but I find the 9m does me from 10k to 20k easily. I use S10 47cm from nicely-powered to over-powered, and a S10 51cm if the wind is very light or under-powered.
If you want two fins (best option) maybe go with the S10 47cm and 51cm. But if you want only one fin, I think a S10 49cm would give the best useful range in most conditions.
I feel that the 53cm will be too much fin under the iS127, and even the 51cm will start to feel big very early on.
All the best