gtx 550 ti is better, only con is power consumption. But for your budget i'd go for HD 6850. The only issue is the psu. These cards are power hungry compared to hd 7750. I am uncertain if you are going to have issues with your psu in choosing gtx 550 ti. If you don't want to upgrade the psu..go for hd 7750. It even works with 350 watts psu. If I was in your position I'd go for HD 7770. It's within your budget and not that power hungry.