Maybe not from a performance point of view, the numbers do not change. But think about it. People look for numbers, do you think that overclocked edition vs. silent edition is anywhere near apples to apples comparison number wise?
Now to the point. Why on earth do these sites even compare OC edition cards to vanilla cards? People care about numbers, so doesn't the OC edition quite much skew the numbers? But hey, it's no secret that the companies themselves ship the OC edition cards to the sites to be reviewed. Even THEY understand that it skews the numbers for them.

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