http://tomshardware.co.uk/2007/05/11/system_builder_marathon_uk/page2.html
An interesting read.
interesting yes, but basically shows that things are still as they have always been.
"Budget" systems end up needing upgrades rather quickly
mid-range systems offer the best bang/buck
top spec systems cost an arm and a leg for less than amazing performance benefits over a well built mid range system.
Oh and if all you care about is games, just through more graphics power at the problem.