Hi,
Gearbox built-in server is only meant for development, it's not meant for production, it's a single thread server.
Adding wsgiref.threaded = true option might slightly improve things as otherwise only one file at time is server, but I definitely suggest you use waitress (by setting use = egg:waitress#main in your .ini) if you want to serve the application through gearbox on production.
About the logging, that's caused by wsgiref itself which gearbox development server uses so it cannot be disabled.