The GTX 670 destroys the GTX 460 SE SLI.
SLI GTX 560 Ti's rapes the SLI 460 SE's and the 670 is still faster than the SLI 560 Ti's.
If you are thinking about upgrading, do go for the 670. It would use half the energy the SLI 460's would use but yet, still out performs it.
2GB of VRAM is another advantage over the 460 SE and this EVGA GTX 670 FTW is a bit faster than a reference GTX 680 that murders the SLI 460 SE SLI.http://www.newegg.com/Product/Product.aspx?Item=N82E16814130802http://hexus.net/tech/reviews/graphics/40613-evga-geforce-gtx-670-ftw/?page=5
Lastly, you don't have to deal with the hassles of microstutter and such with a single GTX 670.