^I wouldn't say it's better than a 670, just faster.
A friend and I have essentially identical rigs except for the graphics card - he has a 7970 overclocked to hell and I have a 670 that's also overclocked as far as it'll go. Although he usually puts out more frames per second than I do, I like my card better, as it's smoother - on his there's a slight feeling of choppiness, even when just staring at a wall with shadows moving.
I keep hearing this... Looking at graphs of the AMD cards they spike and drop much more than Nvidia. I was considering a 670 with 4 GB, but I still don't like the 256 bit memory bandwidth. I like AA and I feel its (256 bit) marginal at best now. Seems like it'll be low in the future.