What are the limits of bitrix scalability?

Question

linux

Hello. The essence of the problem lies in the fact that the scalability on the server cannot rise above 64 pages per second. The test server is running in LSAPI mode.
Exactly the same site, with the FastCGI (nginx + php-fpm) mode of operation, gives a scalability of more than 800 pages per second. We carry out tests on 2 dedicated servers, with the ispmanager panel installed. One has a lite version installed, the other has a business with cloudlinux installed.
The most interesting thing we noticed is that when testing scalability on FastCGI, the load on the server rises to 16-20 la, but on the server with LSAPI (cloudlinux) the load does not exceed 1-2 la, although all cloudlinux restrictions were disabled in control panel using the command:
lvectl set-user username --unlimited
Please tell me what limits the bitrix scalability can rest against?