For a large Drupal site, one of the biggest performance boosts one can do is to install an op-code cache/accelerator. PHP op-code caches / Accelerators Since PHP is an interpreted language, every page access has to load the script, parse it, compile it into op-codes, then execute it. This load/parse/compile cycle can add up to a lot of processing time, specially when you have lots of page accesses. Op-code caches/accelerators eliminate this load/parse/compile time, by doing so once, and keeping the compiled version of the script in memory (or disk) and use it next time a page requests this script.You'll want to especially take a look in the article at the CPU and memory usage comparisons between using and not using op-code caching. The writer also hints that eAccelerator may use less CPU and memory usage than APC. I personally like eAccelerator over APC, but either one is a must have if you run your site on a virtual private server (VPS) or a dedicated server. I run CMS Report using eAccelerator on a VPS I manage through Dakota Hosting.
Bryan Ruby is the owner and editor for CMS Report. He founded CMSReport.com in 2006 on the belief that information technologists, website owners, and web developers desired visiting sites where they could learn about content management systems without the sales pitch. Besides this site, you can follow Bryan at Google+ and Twitter.