What card you should get depends on the native resolution of your monitor so we need to know that before we can make a real suggestion. The cards you are looking at now are generally appropriate for low resolutions and will do an ok job at 1280x1024 and below. The will probably even be able to handle Crysis 2 at those resolutions although perhaps not on high settings or with anti aliasing.
If your resolution is higher than that you will want a better card. Basically it goes something like this:
decent = HD5670/9800GT
good = HD5750/HD4850/HD4770/GTS 250
great = HD5770/HD4870/GTX 260
decent = HD5750/HD4850/HD4770/GTS 250
good = HD5770/HD4870/GTX 260
great = HD5830/HD4890/GTX 275
decent = HD5770/HD4870/GTX 260
good = HD5830/HD4890/GTX 275
great = HD5850/GTX 470
the best = HD5870/GTX 480/HD5970
The two best values for the money right now in general imo are the HD5770 and HD5850. They are well priced, power efficient and DX11 compatible. The HD5770 will likely be ok on your current power supply but I would need to know the model number or the listed amperage on the +12v rail(s) to tell you for sure.