I am currently looking to update my older gaming system one last time and wondering if I currently have the fastest graphics card I can use on this rig or if I can get a better one on here with out bottlenecking.
Current setup is.
Yes, but I believe the GTX 560 has more room for an OC, runs cooler, and doesn't make as much noise.
Either way they are both good, its more of a personal preference thing. The Core2Quad is still an awesome chip; one of my friends is running a Core2Duo still and he is running most of the games he plays on the highest graphics they go, even with a GTX550Ti.
I would go with either the GTX560 Ti or a Radeon 6950. Honestly I would just get whatever one you can find for cheaper or whatever style of cooler you like better. They are more or less equal in performance.