Dont forget some of the older cards can still pull their weight,and will also come with a cheaper price tag too.I use an ATI X800 PRO (256MB) card,and it still gets good comments even to this day.Brand new I bought it for about £200,that was about 4 or 5 years ago,today?,I reckon you could get one for well under £50.
Your new graphics card will probably be that fast you will need to be careful you dont actually create a bottleneck.If your card is trying to pull away like a racehorse and your CPU and memory is not up to scratch you may actually experience degraded system performance.Dont forget cooling solutions inside your case too,as no doubt this card will generate as much heat as the planet mercury
Enjoy the game!