One note about sendfile - if you are using VirtualBox and serving files out of a shared folder with nginx (or I assume Apache) you'll need to disable it or you won't see any updates you do to files once the first version is sent.
Do you have any links specifically discussing the issue?
I then found out that it is actually mentioned in the Vagrant docs also: https://docs.vagrantup.com/v2/synced-folders/virtualbox.html
Google for 'virtualbox sendfile' and there's a lot of discussion.
Worth noting, and this bit me recently, Go's http file handler also uses sendfile beneath the covers.