MSI and ASUS have been sending out review units of their latest graphics cards with higher clock speeds than cards available to consumers, reports techpowerup.
You can access the higher clock speed profile yourself on a retail card but it would require downloading a custom app.
“MSI’s factory-overclocked GeForce GTX 1080 Gaming X graphics card comes with three software-defined clock-speed profiles, beginning with the “Gaming Mode,” which is what the card runs at, out of the box, the faster “OC mode,” and the slower “Silent mode,” which runs the card at reference clock speeds.”
“Turns out, that while the retail cards (the cards you find in the stores) run in Gaming mode out of the box, the review samples MSI has been sending out, run at OC mode out of the box.”
UPDATE: MSI and Asus have both issued statements regarding this issue, stating that their review samples and retail cards are identical in terms of performance and hardware.