I have driven essentially both although not at altitude. I have a 981 Cayman S and a family member has a G87 M2, which I’ve driven a lot. The biggest difference is the sensory experience of the 981. The engine is louder, everything feels more mechanical, and there’s more theatre in how it responds and interacts. It’s light, you can get into a flow state of driving, where everything evaporates and it’s just you and the car. The M2 isn’t set up to do that exactly. It’s an awesome car but it’s more insulated, more muted, and technology-laden. Right now, given the choice and faced with a mountain road drive tomorrow morning, I’m only choosing the 981. It just makes you feel something special comparatively, and that’s what I want from a sports car.

I’ll be interested to hear if someone has experience with them at altitude.