That CM "500W" PSU is overrated and inefficient. I would not trust it to power either of those cards, at least not for long. A true 500W PSU like an Antec Earthwatts or Corsair Builder would be much better choices. Because so many CM PSUs have liar labels, I would not buy ANY CM product so as not to support a dishonest company. Fortunately, in every market they've entered, they have competitors with similar products at similar prices. For example, check out Rosewill cases.
Your CPU is also a little weak, and will bottleneck either card. If your budget allows, you might want to improve that CPU.
If one of your intended games is Rage, be aware that it uses CUDA on an nVidia card to decompress textures, so choose the GTX560Ti.