I know you prolly don't want to hear this, but RMAing a card as defective when in fact you damaged it (by OCing it) is both dishonest and unethical. "Do unto others ...." 😀
The 'right' thing to do would be to call ATI, honestly tell 'em what you think happened, and ask if maybe they can repair it for you for less than a new one would cost.
Not intending to come across as the morality police here -- just honestly trying to help. 🙂
EDIT: I was typing my post as Dave was posting his, so I hadn't seen it. I wasn't intending to pile on, JE78. So now you have an angel on one shoulder saying, "C'mon, you know the right thing to do," and a devil on the other shoulder saying, "C'mon, go for it! Screw ethics! They'll never know!" Quite the unenviable sitch! :laugh:
Good luck, mate. 🙂