XCache and/or APC: what's the best free to used memory ratio
I've used xcache and APC. This question isn't about which is better.
I'm wondering if there's an optimum ratio of free to used memory. For instance, let's say I set the total memory available to 160MB, but XCache ends up using 155MB with 5MB free. Is this good, bad or neither? Should I make available enough memory so there will always be a healthy buffer of free memory? And if so, is there a free to used ratio I should hit, or an absolute number of free MB I should always try to make sure is available?