Hi Paul,
Great tyres you are on now, but not suitable for 10 months of the year! I am a former Met Office weather observer and it might surprise you the mean temperature on the ground where your tyres are in the mornings especially is 6.0 C or below, meaning that a compromise of "all-season" tyres, is just that. I have the same Cayenne living in South Bucks and we run it on winter tyres all year round. Yes, they are wrong in July & August, but right the rest of the year. In the heavy snow last December using the electronic diff lock the Cayenne drove like there was no snow using Michelin Latitude Alpin N1 tyres. Since then I've renewed a pair with the same but now Michelin Latitude Alpin LA2 N0, which are markedly better on a tyre that was already excellent. I change them every 2 years, about 20k plus miles but at 4mm to keep them good for snow & ice. With your mileage of 32k, I think you'd do better than 25k. Too low a mileage? - my reasoning is this - there is no damage you can do to a Porsche that will cost less than the price of a set of quality tyres, before the aggro of getting anything repaired is taken in account too. Once changed DO get the geo checked. You should be able to let go of the steering wheel and drive 30+ metres on a straight road without any steering input. If you are in snow (a skill taught to me by a former F1 driver) and fishtail, let go of the steering wheel (yes really!). Then the caster will instantly straighten the car. I tried this in the snow last year and it worked far better than you'd imagine.
I trust this helps. Perhaps let me know how you get on?
Kind regards,
Richard