2GB refers to Onboard Memory
Superclocked refers to Over Clocked clock speed of GPU and Onboard Memory, mine is 981MHz (GPU) and 1962MHz (RAM).
Regular refers to non-OverClocked
I also own a Gigabyte Radeon HD 6850 1GB and that is 100% OOB and typically 25% to 40% faster than GTX550i, depending...