If you play around with goofy bios updates and unlocking disabled card features, you deserve what you get. If it works, that's fine. But there's a good chance you'll either completely kill your card, or you'll start having massive graphics corruption because those locked pipelines were locked due to being defective.
It's possible for a slightly defective chip to still be released as one of those lesser models, with the bad parts locked out.
There is no free lunch, not on ebay, not with modified bios, and not with overclocking. They all have risks that can result in a completely non-functional part that can't be returned, because you voided the warranty by messing with it.
Yes there's a chance you can bump your performance up a bit, but why not give the thing a chance BEFORE you try to destroy it? Then if it's not fast enough and you're willing to risk destroying it for a little more performance, go ahead and modify it. But give it a chance before you mess with it.