We test several different factors with webservers - how fast it works with SSL certificates, how fast it serves static files, how fast it sends a simple php script, and how fast it sends our test WordPress installation.
In our test between the 2 servers, I get around 70k req/s on static files from LSE and 250k req/s with Nginx. On WordPress without caching (just php opcache) around 800 req/s and on Nginx with a slightly optimized configuration over 1000 req/s. Establishing an SSL connection takes me 16ms on LSE and 11ms on Nginx. I don't have enough experience with LSE for finetuning though.
I find PHP-FPM more stable under high load than lsphp with multiple max conenctions, because if one request is stalled/blocked, it affects only that one request in the process in FPM, but in lsphp it affects all requests in the process. On the other hand, there is slightly less overhead due to the fact that they are in a single process in lsphp.