I'm running Drupal 7.41 & Drupal 8.0.0 on Ubuntu 14.04 with below services:
PHP 5.5.30 (cli)
For better performance, I tried to install and config varnish 4.1.0 + (Vanish module dev version for support varnish 4).
I changed Nginx port from 80 to 81 and Varnish configured on port 80.
This my default.vcl in GitHub:
Please check and recommend for better config.