Because of these dramatic gains, if you have an older PostgreSQL system you'd like to make faster, the very first thing you should ask yourself is not how to tweak its settings, but instead if it's possible to upgrade to a newer version. If you're starting a new project, 8.3 is the earliest version you should consider. In addition to the performance improvements, there were some changes to that version that impact application coding that you'd be better off to start with to avoid needing to retrofit later.
Chapter 16, Avoiding Common Problems, includes a reference guide to what performance-related features were added to each major version of PostgreSQL from 8.1 through 10.0. You might discover that one of the features only available in a very recent version is compelling to you, and therefore you have a strong preference to use that one. Many of these version-specific changes are also highlighted throughout the book.