APC is one of the best PHP op code caches. To be sure its performing the best it can you should monitor its status and make sure it has enough memory as well as correct ini settings.

You want to monitor memory allocated for op code cache as well as user stored items. Its important to get it right as wrong settings may reset your complete cache once it gets full:

You should also monitor the hit and miss ratio for op code file cache:

and the custom user stored items hit / misses ratio:

All you need is cacti and php on your server. You install the script attached and make sure its not accessible from external networks with some htaccess rules.

UPDATE!

Now after some more work and update you can download a combined set of scripts and templates go to the bundle cacti templates page