We are currently using HyperDB which uses wp-content/db.php in order to operate and as such disables the wp-content/db.php from W3TC and stops our Memcached from working.
From reading the support forums a solution may be to use db-cluster-config.php instead of HyperDB. I am just wondering if I am correct in thinking this is a Pro feature.
Secondly, the following thread mentions:
the button does not appear there in the single-blog setups so that is why you are not seeing this and this is going to be fixed in future relases
MySQL Cluster setup
Is that resolved now?