Benchmark Reviews has posted a comparison review between the SLI performance of GeForce GTX 660 Ti vs GTX 670

Back in May (2012) NVIDIA released their $400 GeForce GTX 670 video card, securing the number two position in their single-GPU product stack. Just three short months later, the GeForce GTX 660 Ti graphics card arrived to market and filled store shelves at the $300 price point. With a substantial $100 price difference between these two product, consumers might (incorrectly) presume there's a significant difference in hardware or performance. To the surprise of many, the GeForce GTX 670 and GTX 660 Ti are nearly the same card. Both feature identical 28nm NVIDIA 'Kepler' GK104 graphics processors, complete with 1344 CUDA cores all clocked to identical 915 MHz core and 980 Boost speeds. Additionally, the GTX 670 and GTX 660 Ti also feature the exact same 2GB GDDR5 video memory buffer, clocked to 1502 MHz on both cards. The only physical difference between these two products resides in the memory subsystem: GeForce GTX 670 receives four 64-bit controllers (256-bit total bandwidth) while GeForce GTX 660 Ti is designed with three memory controllers (192-bit bandwidth).

So will memory bandwidth amount to any real differences in video game performance? Most PC gamers have a PCI-Express 2.0 compatible motherboard inside their computer system, although the most recent motherboards and all of NVIDIA's GeForce GTX 600-series feature PCI-Express 3.0 compliance. Additionally, nearly all high-performance video cards feature at least 256-bit memory bandwidth or better (such as 384-bit with some AMD Radeon HD 7000-series graphics cards). However, most testing with these high-end graphics cards has shown little indication that bottlenecks actually occur at the PCI-Express level, even while playing the most demanding DirectX 11 video games. It's more likely that a bandwidth bottleneck might occur at the video card's memory subsystem, where the GPU may be capable of sending more information than the video frame buffer can accept. We discovered some evidence of this in our recent testing on the ultra-overclocked ASUS GeForce GTX 660Ti DirectCU-II TOP, which maintained performance levels with a stock GTX 670 in all but the most demanding video games that featured large maps or virtual worlds.

  NVIDIA SLI: GeForce GTX 660 Ti vs GTX 670