Yes, a GTX 660 is better than a GTX 750. I looked for comparisons, and the differences in various game benchmarks varied from minimal to up to 50% in favor of the 660. The GTX 660 is no longer on the market, but performance-wise I think it would still be considered a midrange card. NVidia's naming convention has never made any sense to me.
If I want to stick with NVidia, it looks like I'll need to spend ~$250 on a GTX 960 just to safely meet the minimum requirements. Even a GTX 950 is not clearly better than the GTX 660, faster in some benchmarks and slower in others.
Now I'm really torn. My left brain says wait until the game is released and see how bad things are. My right brain says go buy a new card now so I can fully enjoy it from day one.