I suspected as much :( Seems like fpm isn't worth the effort after all though sharing the opcode cache by php-fpm workers might be interesting. Thanks a lot for your input!
You're welcome! I'll say though that I did see a boost in response times (can't remember how much but noticeable) when I switched to fpm. So it may still be worth considering, though on CentOS 6 Nginx will be an easier setup and more maintained than rolling ones own. With SSL and official Nginx repo you'll get things like SPDY too.