NVIDIA Corp. (NVDA) today announced two GPUs based on GK106, a variant of the Kepler architecture. NVIDIA's architectural variants increase in number as they decrease in stream processors and features, so the GK106 chips are designed to fill the mainstream niche between the high end GK104 (used in the GeForce GTX 680) and the GK107 (used in the GeForce GT 640).
I. Digging Into the GTX 660
The bottom line on the GTX 660 performance wise is that at $229 USD is narrowly the best buy in the $220-$240 bracket.
It trades blows with Advanced Micro Device, Inc.'s (AMD) Radeon HD 7870 (a Pitcairn architecture), which is also typically available for as little as $229 USD, with discount.
In benchmarking by AnandTech the GTX 660 generally outperformed the HD 7870 at lower resolutions, while falling a bit behind at higher resolutions.
Sources: NVIDIA, AnandTech