[eluser]Twisted1919[/eluser]
Forget APC . Go with Xcache .
I recently used it on one of my servers and the result was unbelievable .
From 5 Mb/req i went down to 0,7-1,5mb on high load pages . The loading time decreased from 0,4XX-0,9XX to 0,077-0,1XX .
BTW, i don't believe that building an application from zero on top of APC / Xcache / Memcached is a good idea.
Your app must scale in normal conditions , and apply these changes ONLY when your server is a powerful one and can't handle all the requests any more .