Best configuration for wordpress based site

As @vegardx already explained a good way to load your WordPress based website faster however only server configuration can not make your WordPress site fast… Your can use Free WordPress CDN which can decrease your loading speed 3 times. It based on W3 Cache plugin self hosted Content Delivery Network

When you’re using a reverse caching proxy it doesn’t really matter what you’re using on your backends. As long as you’re familiar and used to it, it’ll do. I prefer Nginx, simply because the configuration is a lot more clear.

Now - back to all the other names you’ve dropped. Most of them do more or less the same, just with a slightly different approach. I doubt you’ll see much difference between XCache and APC, they are both opcode caching.

Memcached is cool if you have multiple nodes and want a shared cache, but given that you only have one, I don’t really see much gain in using it as a key value store over, say, APC. APC is both a key value store and opcode cache.

Using a different (cookieless) sub-domain for a pseudo-CDN can give you slightly faster load times as you trick the browser into opening more connections in parallel to your server. I wouldn’t spend much time on this before you’ve settled on a proper reverse cache and chosen a opcode cache.

You can never go wrong with Varnish, but it adds a little complexity to your stack. If you have more or less only anonymous traffic (ie. not logged in) Varnish will solve all your issues, as long page renders will hardly ever occur anyway. There is also a plugin to Wordpress that integrates it with Varnish, so you can clear the cache when posting new articles and such.

Simply put,

nginx with it’s built in caching.

This negates the need for any back end tweaks or extra processes like memcache etc.

If you have lots of logged in content then I would run the latest and greatest php5-fpm which already has zends opcache built in. The opcache will cache all php queries from nginx which should speed things up nicely while keeping cpu processes down.

The above setup should negate the need for you to mess about with mysql although you should make sure that the mysql query cache is enabled :)

Good luck