I can see this is going to be difficult...
What about the settings? Are you using 8xAA? Take a quick look at this.
http://www.chiploco.com/sparkle-geforce-gtx-550-ti-1gb-review-5312/6/
Lowest res they use is 1600x900. Its bigger then your 1024x768, but they probably use a faster CPU as well so depending on your system it might be close to what you get. The 550TI is not a monster gamer. It gets barely 30FPS in a game you mentioned. That's why I asked the questions I did in my first post. GTX550TI having problems? Not a big surprise if you are playing recent games at high settings.