A pure race sail does indeed hammer the board more down and better loosens up in overpowered airflows.
This is exactly what you want when you're riding in heavy chop.
I think that every cambered sail will be more stable in any kind of wind (low or high end) c/w a non cambered sail. Some people like the non cambered sails because they find they can jibe easier with it, while I think that a cambered sail helps me better "pull" through the jibe turn. It's true of course that the cambers will make the sail turn over a litte bit slower, with a little extra effort of the rider. Non cambered sails have only 1 advantage, according to me, i.e. they waterstart a lot easier.
Personally, I use a 9.5m2 sail on my IS122 in 12-15 knots. It goes amazingly well. I'm 85 kg.
If the wind gets very unstable I use that same sail on my F161, which helps me a lot planing through the lulls and going upwind.
If the wind drops to 8-12 knots, I use a 11m2 sail on my F161. Works amazingly.
In your case (and this is my personal opinion), if you don't want to buy a bigger sail than 9.2m2, I would go for the IS127 or perhaps the new IS117 wide. If the wind drops under 12 knots, you really need an 11m2 sail + the IS147 or formula to get going.
The IS127 will also be perfect with the overdrive 8.5 when the wind picks up.
Good luck with your choice.
I know how hard it can be.