I know. At one point, we were using one of them to monitor a PGP server we have at work, as we needed something"off network" to check SSH was still running, and I was only using the smaller VPS as a Nagios monitoring box.
Generally Nginx > Apache. Litespeed and Nginx static file serving pretty close. Litespeed LSAPI PHP > Nginx php-fpm in terms of scalability though on pure PHP processing without any caching. (especially if you're confined to a single web server only and not a cluster of web servers).
I don't use Nginx built in caching via fastcgi_cache, but maybe Floren can share some pointers as he has success using it for Xenforo