I have been reading a while the web trying to find out about opcode caches for fcgid. As I understand so far APC is not a good solution for fcgid, since APC with fcgid caches only per process and that is inefficient. (ref: https://stackoverflow.com/questions/598444/how-to-share-apc-cache-between-several-php-processes-when-running-under-fastcgi)
So I guess that leaves eaccelerator and xcache. Xcache seems to talk explicitly about fcgid so I am leaning towards that. Can someone confirm this?