Wordpress performance - W3 Total Cache and memcached/APCu

I have freshly installed Wordpress, Nginx with PHP-FPM, W3 Total Cache (plugin), memcached and APCu on PHP 5.5.

I will run a benchmark on my local mac against the aforementioned AWS server using Apache Bench (ab), I get a consistent 240 Requests Per Second (RPS) with test.com poisoned to this server, or around 40 million hits per day according to blitz.io. Keep in mind this is with the default Wordpress theme.

This performance is great and outperforms almost every (not all) blog post out there regarding performance. I have spent a lot of time and research getting to this point, but now I have a couple questions regarding APCu and Memcached.

Once we go to another heavier theme (have tried several), performance drops and I cannot tell whether memcached is even functioning.

1. Do I need both memcached AND APCu?


2. We are having some database performance issues. How can I tell how well memcached is functioning (what rate cache is purged at, hit and miss rate, etc)