That didn't answer my question. First the Geforce 550 TI i choose have a faster Core clack and double the memory clock, so i dont see how the card you choose is better. Yes it is 256-bit as apposed to 192-bit but that's about it.
If you have your heart set on a gtx 550 ti, go ahead and get it. I'm not saying that it's a bad card, I'm just saying that the 6850 is a better card, and it is around $150.
As you can see, the 550 ti is more comparable to the 5770.
If you really want to go Nvidia, you can get a gtx 460 1gb for around the same price as the 6850. The 460 and the 6850 are pretty much on par with eachother.
EDIT: Put the chart with your version of the 550 ti in.