[glc]

From that article, last page:

As far as performance goes, the first clear group of GPUs includes the GeForce GTX 650 Ti Boost 1 GB and below. You see a great correlation between speed and cost up to this $150 card. Every dollar you spend yields a commensurate return in performance. In the value-oriented segment, that's exactly what you want to see. After $150, the $170 GeForce GTX 650 Ti Boost 2 GB doesn't deliver much extra at standard settings, although the additional gigabyte of GDDR5 sometimes helps at high resolutions and more demanding detail presets. The GeForce GTX 660 is a good intermediate $200 step before the $250 Tahiti-based Radeon HD 7870. Beyond that point, price increases faster than performance, negatively affecting absolute value. Having said that, if you're a hardcore gamer who desires high resolutions and taxing detail settings, cards like the GeForce GTX 670 or Radeon HD 7970 will make the difference between playable and unplayable frame rates.