In terms of overall gaming performance, the graphical capabilities of the Nvidia GeForce GTX 980 Ti EVGA Hydro Copper 6GB Edition are very slightly better than the Nvidia GeForce GTX 660 Ti 3-way SLI.

The GTX 980 Ti has a 225 MHz higher core clock speed than the GTX 660 Ti, but the GTX 660 Ti has 160 more Texture Mapping Units than the GTX 980 Ti. As a result, the GTX 660 Ti exhibits a 106.8 GTexel/s better Texture Fill Rate than the GTX 980 Ti. This still holds weight but shader performance is generally more relevant, particularly since both of these GPUs support at least DirectX 10.

The GTX 980 Ti has a 225 MHz higher core clock speed and 24 more Render Output Units than the GTX 660 Ti. This results in the GTX 980 Ti providing 43.5 GPixel/s better pixeling performance. However, both GPUs support DirectX 9 or above, and pixeling performance is only really relevant when comparing older cards.

The GTX 980 Ti was released over a year more recently than the GTX 660 Ti, and so the GTX 980 Ti is likely to have better driver support, meaning it will be more optimized for running the latest games when compared to the GTX 660 Ti.

Both GPUs exhibit very powerful performance, so it probably isn't worth upgrading from one to the other, as both are capable of running even the most demanding games at the highest settings.

The GeForce GTX 980 Ti EVGA Hydro Copper 6GB Edition and the GeForce GTX 660 Ti 3-way SLI have the same amount of video memory, but are likely to provide slightly different experiences when displaying game textures at high resolutions.

The GTX 660 Ti has 96 GB/sec greater memory bandwidth than the GTX 980 Ti, which means that the memory performance of the GTX 660 Ti is massively better than the GTX 980 Ti.

The GeForce GTX 980 Ti EVGA Hydro Copper 6GB Edition has 2816 Shader Processing Units and the GeForce GTX 660 Ti 3-way SLI has 4032. However, the actual shader performance of the GTX 980 Ti is 4668 and the actual shader performance of the GTX 660 Ti is 3951. The GTX 980 Ti having 717 better shader performance is not particularly notable, as altogether the GTX 660 Ti performs better when taking into account other relevant data.

The GeForce GTX 980 Ti EVGA Hydro Copper 6GB Edition requires 250 Watts to run and the GeForce GTX 660 Ti 3-way SLI requires 450 Watts. We would recommend a PSU with at least 600 Watts for the GTX 980 Ti. The GTX 660 Ti requires 200 Watts more than the GTX 980 Ti to run. The difference is significant enough that the GTX 660 Ti may have an adverse affect on your yearly electricity bills in comparison to the GTX 980 Ti.