For years I had been using shared hosting. On my recent host I noticed that Xenforo site is working slower when I enable file based cache. In the recent weeks I moved the site to VPS and I noticed the same unusual behaviour. Similarily, enabling APC or Xcache in config.php is making the site a bit slower. With both Xcache and APC I noticed that the site got siginificantly quicker just after installing and running either of them on the server, without configuring cache in config.php. Perhaps there are some server settings that I should take care of? Currently I'm running Xcache and Xenforo is being cached nicely without the cache being configured in Xenforo's config.php. I'm going to leave it at that.