ExtremeTech has compared 23 processors from AMD and Intel. They tell you which CPU offers the best performance per dollar for various tasks, including office productivity, 3D rendering, gaming, media encoding and more.
Trying to determine the sweet spot where price and performance cross over for CPUs is a more daunting task. For one thing, the applications mix is far more complicated. People use office applications, create content for web sites and games, encode video for building DVDs, and play games. Each application mix may have different issues when it comes to determining the optimum price/performance ratio.