Always good to monitor Zend Opcache usage. I wrote my own script for my Centmin Mod paid clients that allows me to break down usage per domain name too
On a roll, new charts for key and strings buffer usage pie charts were added. I also added a Zend Opcache memory usage line chart over time derived from logged data that survives PHP-FPM restarts and also annotates labels when the PHP-FPM service is restarted
phpCacheAdmin is my goto for cache tuning and monitoring. Its web dashboard covers Server info, PHP info, Redis, Memcache, OpCache, APCu, and Realpath info. They just put out a decent update a few days ago also.