Hi there,
I really enjoy your tutorials so I thought I'd give you some suggestions for future tutorials :-)
nginx+ WP + redis cache see: http://www.jimwestergren.com/wordpress-with-redis-as-a-frontend-cache/ and http://www.jeedo.net/lightning-fast-wordpress-with-nginx-redis/
nginx+naxsi - it looks like naxsi is the equivalent of mod_security for nginx and would be very useful.