Killer question to ask, and there will be a huge amount of responses, mostly all un proven, just gut reactions.
My 2 p here is little more than that too...
I have a humble 2.9 987.2, nothing fancy and I don't drive it like I've stolen it, I have a race car for that.
I seem to be surrounded by Shell stations, BUT this is not the case everywhere.
I got caught out in Wales once and filled with Total 95 RON. Car just drove like it did with the then 97 RON Shell V Power.
When 1/2 empty, filled with V Power so a mix of octanes, no perceptible difference, car ran great, but I was not thrashing it. (wife on board)
Always try to use Shell 97 RON, just think it is a the best fuel, maybe I'm a sucker for the adverts?
Last year in France in the car and filled many times with French motorway brand fuels, some 99 RON, no difference, just price.
A Porsche friend works in QA for Bentley. He said when those cars go performance testing over the world, the fuels they are forced to use can be near any RON and all is well.
The car have to tolerate the variations, why modern cars can self-adjust, and do, to what you pour in.
In general I believe Shell V Power is a very consistent fuel so I take the price hit knowing the best (in my opinion) is in the car.
I use it in my 1973 911 and it feels to make quite a difference to that cars 'feel' compared to Shell 95, and I use it in the Porsche air cooled race car too that is always thrashed as hard as possible!
I think just use good 'names' fuel, 95 ron minimum and enjoy the drive. If you are going racing? V Power every time.
All imho of course.