In the post WordPress Caching Comparisons Part 2 Matt Martz compares different caching setups, among them APC object caching together with Batcache page caching. In his post this combination seems to be the best tradeoff between setup complexity and efficiency. He doesn't mention memcached so I'm unsure if it's used or not. From reading Mark Jaquith's post APC Object Cache Backend for WordPress it seems to me that his plugin works as a drop-in replacement backend to be used in place of memcached which is what the Batcache installation instructions says to use. This is also how it has worked in my experiments with these plugins. I.e. either the APC or memcached backend is used, but not together and in combination.
However, from watching Iliya Polihronov's High-performance WordPress video (and this is where I started when looking into caching) I got the impression that APC object cache can be used for opcode caching in combination with Batcache/memchached for full page caching, for even better results. (the batcache discussion is at the very end of the video) Is this possible and would there be of any benfit, or am I just confused?
In my case I'm looking for the best solution for multiple virtual single-WordPress servers (i.e. not multisite) served by a single webserver (nginx). This runs on solid state media (Raspberry Pi/SD-card) so it would be preferable to keep cache in memory. I have full access to the system and have apc, memcache and memcached extensions installed.
edit: From reading the Batcache source my understanding is that Batcache uses whatever is offered by
object-cache.php, so it's either APC or memcached object cache as used exclusively by the respective backend plugins.
Also, I found Matt's definition of bytecode, object and page caching at the end of his post enlightening.