Your question was also my biggest concern with the US 147.
Like you I weigh +/- 88kg.
I use a 10.9m2 Gunsails Mega XR as largest sail.
It works excellent.
I understand you very well when you say that you find a freerace sail like the Overdrive sometimes overpowered in the gusts. I had the same problem even with my old 9.5m2 gunsails Booster freeracer on my former Formula 161.
When I purchased my 10.9 Mega XR full blood race sail, I started realizing what these sails can do.
They remain stable in gusts and are much longer controllable. I've told this story already several times on this forum. I can recommend every intermediate/advanced windsurfer to use full race sails. They make life much easier and only have 1 disadvantage, i.e. they are heavier to carry to the water. Once you're sailing, they only have advantages according to me.
Because the US147 felt so light under my feet, I was also worried in the beginning how it would handle such a heavier Full race sail, but I was very impressed. It handles it perfectly ! Even a 12m2 would be possible according to me. But what you also need with this kind of bigger sails is a bigger fin. I find the standard 58 fin not powerful enough. I've recently purchased a deboichet 64, which should be good, I hope. I couldn't try it yet.
Personally, I think the 10.7 reflex will be very good,
IS87 / IS101 / IS122 / US147