Okay so there have been reports, or rather rumors, of Radeon RX 480 cards operating at 1.5GHz without an issue. This could be true, but it certainly wasn't the case for my reference card. After a heap of messing around with AMD's new WattMan I arrived at a pretty dismal 1350MHz, a meager 7% overclock. Even at this frequency the fan spun right up after a few minutes and was much louder than we ever experienced when overclocking the GTX 1080 Founders Edition card for example.
Of course, the RX 480 reference card has been fitted with a pokey little heatsink. Just to make sure we weren't being thermally limited I cranked the fan to maximum speed. The amount of air this thing moves is incredible, though it sounds like a Hoover doing it.
Anyway, with the fan maxed we still couldn't get a stable overclock beyond 1350MHz.
It's a shame we couldn't get much out of our sample. It would have been nice to achieve R9 390X-like performance in Far Cry Primal. Still, the overclock did net us 8% more performance as it took the average frame rate to 42fps, allowing the RX 480 to match the GTX 980.
Doom also saw an 8% performance boost from the overclock -- enough to overtake the R9 390X this time, but not the GTX 980.