Hello Dear fellows this is a Discussion on the comparison of GTX 660 and GTX 480.
I once read a thread on Tom's on the same topic and it was left without a conclusion.
Well let me make this clear as I think I can answer the question correctly. (We will make it short)
The GTX 480 is Fermi architecture Card while the 660 is based on the new Kepler architecture.
The GTX 480 has the advantage of greater memory bus that is 384 bit and MORE Rops (that is more Pixel fill rate).
The GTX 660 has the advantages of GPU Boost , TXAA , FXAA , More Cuda Cores , Greater bandwidth , greater Texture fill rte , Running considerably cooler , drawing less power and more TMU's , better Open GL support .
Now Lets talk about the G3D Mark.
GTX 480 Average G3D Mark Score of 4350.
GTX 660 Average G3D Mark Score of 4118.
The GTX 480 scores a bit better in Gaming in average conditions but the More Cuda Cores and TXAA and FXAA technologies will help GTX 660 remain the winner against GTX 480 (In games like Watch Dogs).
So given the above circumstances , it is clear that even though GTX 480 beats 660 by a small margin in present-day games , It will actually end up the runner up in the Future.
However for Guys with a GTX 480 right now , upgrading to a GTX 660 WILL NOT see a great boost in games.