The GDDR5 is faster than the 6670, but I'm not sure of the actual gain in performance. I would post one of those charts that compares performance, but I have no idea how. Anyone else who posts on this forum who knows how if they want to enlighten me that would be great
If the card is going to be used for gaming, like alot, it might be a better investment for the GDDR5. If it is more for light gaming, then the DDR3 should be fine.