The 192 bit bus width might end up becoming a bigger choke point as the requirements change depending on how long you plan on keeping your 660 for a 2 monitor setups. If you can stretch your budget a 7950 would be more likely to play newer games on higher settings.
If you can't stretch your budget and you live in the united states i would higher recommend this HD 7870 Tahiti LE. It is the same chip as the 7900 series and has better specs then a normal HD 7870. It still has less V-Ram then a 7950 but would still be a lot faster then a GTX 660 even at stock clocks. And the AMD card has a higher overclocking headroom so if you are looking for something to keep up with newer games it would be better.
It is the same price as the GTX 660. But newer games might also be more and more optimized for AMD graphics as well with both the Xbox One and PS4 using AMD CPU's and GPU's but that's just speculation I guess. If you don't live in the united states look around where you live on Tahiti LE 7870 prices.