They tested an oced version of the 7770 where they didn't encounter a 30% difference MAX, let alone average.
They don't test based on frame rates they did test on what a gpu delivers. In their case they didn found any difference between the 6870 and 560 and 7770oced version when playing games. All three were smooth with the same settings, none of them were playable with higher settings, ergo their would be no difference for them running a 6870, 7770oced or a 560.
They do mention that its a strange scenario because the biggest competition for the 77xx series are their own previous series which have dropped in price dramatically.
But yeah you don't read it... so you shouldn't judge reviews you don't read... (i assume you didn't read it because you fail to grasp even 1/10th of what they mention in their review...) E.g. the one with a bias is you...
I didn't read the review, HardOCP is not on my list of reviews when I evaluate a card but I just did now since you pointed. It's downright laughable. Let me quote:
"The cheapest GeForce GTX 560 Ti can actually be had right now for $189, or a Galaxy GTX 560 Ti for $197 or a Gigabyte for $209. The GTX 560 Ti is more expensive than the XFX R7770 Black Edition, yet in our gameplay testing we have discovered that the gameplay experience is the exact same between these two! The less expensive XFX R7770 Black Edition produces the same gameplay experience as the more expensive GTX 560 Ti. This is amazing, and is the exact definition of value for your money. Yes, the GTX 560Ti is technically faster than the R7770 in most of the games we tested but those frames did not pay off in a better gameplay experience."
So the reviewer is basing his conclusion (overclocked card vs. stock) on
"the gameplay experience" whatever that means. The GTX560Ti is in another league together with the HD6950 and stock vs. stock it is on average 40% faster. So he's acting like a sales agent trying to convince us that an 180$ card (which is the price of the 7770 OCed version) is competitive with a 190$ card when in fact there is a night and day difference between the two. That's all, I will end my intervention quoting again the aforementioned sales agent:
"This is amazing, and is the exact definition of value for your money"