Why is this APC installation failing so badly?
When using APC one of the things you need to ask yourself how much memory will be allocated to APC. apc.shm_size controls how much memory will be allocated. All my setups are configured to use 30M (I believe 32M is the default option). Also, check your "cache full count" to ensure APC is actually working. This shows how often the cache is at maximum capacity. If the cache is constantly being filled it will certainly take a heavy hit on your scripts performance. You could also try allowing PHP to use more memory as a test case