DD did not take up SPGS, so we couldn’t comment on the environment.
I’m sure whenever you ask this type of question on MN, you will see some mums jump in and give you euphoric personal experiences that counter every single concern you might have, albeit occasionally hear some odd negative experience thread will get shut down quickly by the same group of mums.
So perhaps do not take it with a pinch of salt, for any schools, get the offer first, then try to find out more on the offer holder day, talk to the real kids and parents that in the same situation as you and get a feel for how it is and fit. Every child is different, anecdotal information (like you concerned stressful environment in the first place) may have no ground. On the other hand, limit your view to just one or two “direct experiences” in MN is not helpful. Try to gather information from various sources to make a proper informed decision. Good luck.