I guess the configuration is crystal clear and it explains everything in pure english, the notable part might be gzip_comp_level which describes the compression level of gzip, it can be between 1 to 9 with 9 being best as of the time of writing. If you want to see the result of different level of compression then phrogz.net has some valuable benchmark result.
Other thing to consider is gzip_types where you can define the mime types that you want gzip to compress.
Gzip static is the most lovely thing here, usually when you are using gzip it only compresses the file in the client site, but gzip static is different beast. Normally with Gzip the server request works like this:
Browser Makes the Request -> Server Receives the Request
Server compresses the file to serve -> Browser receives compressed file
With each request server has to compress the file, which takes some CPU resources and also increases the latency. But with Gzip static, server stores the compressed file in it and when:
Browser Makes the Request – > Server Receives the Requests
Server Sends the Compressed file -> Browser receives the compresses file
This how more latency/bandwidth will be saved with gzip_static on.
To use gzip_static on, you have to compile Nginx –with-gzip-static