I’ve turned a lot of laps at Mosport with PCA in a 930 street car, a 930 race car, a 964 race car and a lightly modded 2007 Cayman S. So a good amount of experience without any driving aids, and a couple of seasons with PSM fully engaged in the Cayman.
When driving the Cayman, every time I’ve decided to lift out of the throttle slightly (as I would in one of the air cooled cars) because things were about to go south, the car thinks the exact same thing and beats me by a fraction of a second. So myself and the car are thinking the same thing, at the same time (and the car will always be faster to react). In the aircooled cars I am the input.
I don’t see the benefit to turning it off, especially for what we are doing. What do you stand to gain vs what you are risking? It hasn’t slowed me down, and usually if you manage to upset the car enough that PSM is engaging then you’ve made a mistake or taken a sloppy line through a corner.
There is only one place where I can routinely get it to engage and that’s the exit of 5b, but it’s usually just too much steering input on my behalf upsetting the car. Turning it off to gain a small amount in that corner and risk a bigger mistake elsewhere just doesn’t seem reasonable.
Any Porsche Stability Management system from the last ~15 years or so is very good and not that intrusive. It doesn’t completely sack the car of its power and allows a LOT of room. So I would vote to leave it on.