HTTP connections are fast from local network, very slow from the outside world

That's because you set up your Wordpress server to redirect to your internal IP, 192.168.0.173. So when external clients try to reach your Wordpress server, they are being redirected to http://192.168.0.173/wp-login.php which will, of course, fail after a timeout. The same goes for your Wordpress homepage, there are a number of resources, like CSS and image files, that are being served from http://192.168.0.173 instead of http://aarroyoc.noip.me.

The reason why PHPInfo works, is because it's completely self-contained. Even the PHP logo is embedded into the HTML. Check the source to see what I mean.