This is more of a question to clarify my own curiosity than a support one.
If Xcache is an opcode caching mechanism, how does this help serve static content out of memory? If I keep my page cache set to 'Opcode: Xcache', am I in fact still dynamically generating pages every time, simply with the benefit of the opcode being pre-cached already? Or is there some other feature of Xcache that you're taking advantage of, where it does memcache-like caching of the output of whole URLs e.g.?
I was intrigued by your recent comment that single server sites might want to try advanced file based caching after all.
I'm running W3 Total Cache on nginx with Xcache set for a 128 meg cache size for a small blog right now. At 64 megs, the Xcache admin panel would still show the PHP cache max out after less than half an hour.