Glad to know you are interested in knowing about web performance. Here, you may read posts on Nginx, Varnish, Apache, hosting, or security (many ignore the security while thinking about performance; I don’t). Or would you prefer some videos? :-)
When thinking of SEO, it is hard to ignore pagespeed of a web site. This site, particularly this home page scores 100% on PageSpeed insights for both mobile and desktop!
SPDY, Varnish, or memcached may not be as famous as PageSpeed. However, all these (and more) are deployed here to speed up this WordPress site on supported browsers. No wonder, this site has got a Google PageRank of 4.