Caching the bytecode of the PHP scripts will give a speed boost. Not much of one, since parsing the code is very little of the response time compared to the time needed for big queries to CQP or MySQL, but every little helps.
This should happen automatically if the APC extension is present and working. All that is needed is some tricks for monitoring and controlling the cache, and some notes on installing/configuring/using in the setup manual.
The admin control panel will need a little control on the PHP settings page, allowing the cache to be cleared manually (e.g. if the scripts are updated); (also detecting whether or not the extension is present, what pages are cached....)