Dynamic sites and hosting limits: PHP Workers VS User Processes Per Sec Limits

I have an e-learning site hosted at Siteground on their scalable Google Cloud platform and have worries about hosting performance if / when my site begins to have 100s concurrent users (for example if all taking online tests at the same time).

My understanding is that PHP workers are a big factor when it comes to the performance of sites with dynamic content (e.g online quizzes).

I know Kinsta hosting wrote a blog on this and recommends at least 4 PHP workers for membership/e-learning sites and they limit PHP workers on their tierd plans.

When I asked Siteground about PHP workers, they said they do not limit them. Instead they limit user processes per second. Default is 40, but they have raised mine to 100.

My question therefore is, which hosting environment (limiting PHP workers or limiting user processes per second) offers a better set up when hosting sites with dynamic content?