I'd recommend CFengine for any environment which is more than 2-3 boxes and where you have some concept of 'templates' or servers performing specific roles.
Why? Simply put it reduces mistakes, you have a tool which will ensure file/directory permissions are correct everywhere in the environment and when you come to roll out more servers, the tool handles absolutely everything and never makes any mistakes.
Contrast with even a skilled System Administrator rolling out a web server at the end of a twelve hour shift when things already went wrong.... Are they likely to remember that nasty little configuration file which needs to go in /etc/random/location/foo/bar otherwise the application will silently fail to do something rather important, like bill customers? :)
Tools like CFengine are also a great way to perform environment-wide security updates. Dropping a Nagios configuration (NRPE) onto all boxes is also a doddle. Whether you're dealing with five boxes or five hundred boxes you will save time with CFengine.
It is probably worth noting that my environment is a little larger, however I've also deployed CFengine for smaller environments than you note, hence the recommendation!
Probably your next question will be CFengine vs Puppet? That's a more difficult decision, and I've always gone CFengine due to (in the early days) some immaturity from Puppet, particularly around error logging.... these days I'm really not sure - have a play 'n see? Looking back to my specific issues with Puppet, they were SSL certificate related, painfully still recall the time I spent 3 hours diagnosing server <-> client connectivity issues in irc.freenode.net/#puppet with some hefty RTFM and RTFS only to find an error, not being logged, and Luke said, "Ah that's really difficult to fix" and never did. :(