Hi, I have:
nginx 1.11.3
Ubuntu 16.04.1 LTS
openssl 1.0.2g-1ubuntu4.5 amd64
libssl1.0.0:amd64 1.0.2g-1ubuntu4.5
weak CPU: N3150
16 GB RAM

with this test-setup:
open_file_cache max=1000 inactive=360s;
open_file_cache_valid 30s;

I test on running ab command on the same host as nginx is.
For a 1.6KB text file I get 4600 req/s with http and 550 req/sec with https. I get the same using or not gzip encoding.

Why is this huge performance difference?