When I built my current system 2yrs ago, I used Tom's Hardware for quite a bit of the baseline info. They run roughly quarterly features where they put together 3 complete systems at different price points (varies, but last one was ~
$500, ~
$1200, and ~
$1600.) They then have an overwhelming amount of benchmarks on the three systems from several of the popular gaming titles, and give you a decent idea of what extra you get for your dollar.