When OCed, the GTX460 performance is quite similar to the HD 6850.You can easily get the dimensions by checking with the manufacturer's website.
Too right, my friend said that it can be faster than HD 6850 if OCed. But i'm sorry, like i said - i'm not an OCer.
Oyea i can get the GTX 460 dimension from the official website, but for the HD 6850 - i have no idea for this one
And what about if those cards compared wiht the HD 5830?