What are the specs for your current system? Also, what games are you playing?
By the way, having a video card with DDR3 memory has nothing to do with the type of memory you have installed in your motherboard.
Be sure to provide the make/model of your power supply and motherboard in your system specs.
While gathering this info. Consider this GPU:http://www.misco.co.uk/Product/173788/Sapphire-Radeon-HD6670-2GB-PCI-Express-Graphics-Card