Which combination of web server (IIS/Apache/nginx) and PHP (fpm/fcgi/mod) will be the most productive on Windows?

Question

PHP

Type: internal corporate site (laravel)
OS: pure Windows Server 2012 on VDS
Hardware: 6 GB of RAM, some Xeon for 4 cores, SSD
Permanent online: from 20 to 200 people.
PHP: 7.1 + opcache
Problem:
They allocated a clean server so that I could transfer our project from another one.
The old one (specs above) worked on IIS + FastCGI. There was a problem: with 150 people online at the same time (in addition to loading the page, each of them has ajax every 10-20 seconds), the CPU goes to 100% and the server goes down. I would like to set up a new one as productively as possible, so that it can hold at least 200 people. I don't have experience here. I have always used nginx + php-fpm on nix. But in a company you can’t even install a virtual machine with Linux.
Attempts:

1. nginx could not be adequately configured: for some reason it uses only 1 core out of 4.
   
2. apache + mod_php + mpm_winnt - set threadsperchild 150 and 300 - I don't even understand how many threads should be set in my case?
   
3. iis + fast-cgi for 4 processes (right?)
   

Question:
For the last 2 cases, I tested: ab -c 5 -n 3000 on an empty Laravel helloworld (the one after a clean installation of the framework). And even 5 simultaneous requests load all the cores by 95-100% until the test is over. Is it supposed to be like this or what am I doing wrong?

Answer 1

Considering that this is Vidna and Laravel is not the fastest framework - yes, it's normal.
So what is the average response time to a request?

Answer 2

The problem is clearly not in the hardware (if not overselling and there is still a supply of resources on the VDS farm), but in setting up the network on the VDS side.