Depends on the games. If the games supports SLI very well, it's likely 550 ti SLI's going to be better. For others, 480 is going to be better. But still I will avoid 480, except these two is actually the two cards you can get, There is still better card than 480 like 6970, 7950, 570, etc. If you have the 550 ti already with you, it's better to SLI it and save money.