Would you mind to try Nginx caching in Plesk Onyx 17.8 Preview?
This would be very helpful to get your experienced feedback here http://www.surveygizmo.com/s3/4165754/Plesk-17-8-Preview
An error occurred while saving the commentdan pin commented
I tested another panel with apache+nginx+varnish. Varnish with cache in RAM, websites have great speed with this config. Of course, this panel is not as safe and complex as Plesk.