APCu, OPcache, Varnish & Memcache together?

What reported in the project page is always valid.

Use the cache implemented by this module for caches that do not change often and will not grow too big to avoid fragmentation. The default setting of APCu will allow you to store 32 MiB. Make sure you tweak this according to your website's needs. An example configuration could be to cache cache and cache_bootstrap in APCu, cache_field and cache_menu in Memcached, and store cache_filter in the database.

It cannot be more specific, as giving suggestions that are valid for all sites is quite hard.

OPcache is an opcode cache. It makes the code run faster because it caches the opcode the PHP interpreter generates from the PHP code. It does not conflict with APCu, which only caches data.

Varnish is a s a reverse caching proxy. It caches the pages produced by a HTTP server. It does not conflict with APCu. It eventually avoids a page is generated by the server and it lifts off some work from the HTTP server.

Automatically closed - issue fixed for 2 weeks with no activity.