Every time there is a noob post, a good chunk of members can't control their need to suggest spending more than the OP's budget; that is not helpful, it is possible to tell it like it is without giving an opinion.
GrandZechs
So building my new rig, Just trying to decide between the 660ti sc 3gb SLI or 670 2gb SLI. Is there a big difference when going to the 670's? 3gb of 192 bit or 2gb of 256 bit memory seams to be the only difference, I just don't know which is better.
If you don't plan on overclockng, then the 670 is faster by virtue of the higher memory bandwidth as plenty of reviews show that the 192-bit interface castrates the rendering ability of the GPU even though both 660 Ti and 670 have the same number of CUDA cores. The higher Vram doesn't compensate for performance losses.
If you intend to overclock, you can remedy the issue with the interface, all you have to do is overclock the 660 Ti's Vram to match the memory bandwidth of the 670.
Interface width multiplied by effective frequency divide by 8 = memory bandwidth; so you'd need to overclock the 660 Ti's Vram to
8GHz effective, at that point the 192-bit interface won't bother you anymore:
Stock 660 Ti SC : 6GHz x 192-bit ÷ 8 bits per byte = 144GB/s
Stock 670 reference : 6GHz x 256-bit ÷ 8 bits per byte = 192GB/s
OC's 660 Ti SC : 8GHz x 192 bit ÷ 8 bits per byte = 192GB/s
Since the core specs are the same between both cards, for the most part since the SC model is set a bit faster, if you manage to overclock the Vram high enough as shown above, you make the cards alike and thus the 660 Ti benefits from the 3GB Vram. How easy is it? It isn't, most folks are able to achieve 7GHz; overclocking isn't guaranteed, it is luck of the draw; but even if you get close, it makes all the difference because you're making up for lost memory bandwidth.
Moral of the story:
- If you don't intend to overclock, get the pair of 670's
- If you do intend overclocking, get the pair of 660 Ti's and crank only the VRam as high as you can manage stably.