I notices in global configuration I only have the option to select APC if I turn on progressive cache. However, while progressive cache seems to work once upon refresh my website goes wonky namely roksprocket displays all 3 showcase items stacked on top of each other. I switched back to conservative cache / file and the issue was gone I could refresh all day. Next I went into the file explorer and changed cache handler in configuration.php from file to 'apc' even though it wasn't an option under global configuration is this allowed?
If APC is available with Progressive cache I don't see a reason why it wouldn't be available with Conservative caching. As a side note, that issue with Progressive caching is actually a Joomla core bug which has been reported to the Joomla core dev team