While AMD's refinement of the 14nm process may have opened up some additional frequency headroom, most of that has already been eaten into by vendors to help make RX 580s faster than their predecessors.
In the case of this Sapphire card we were not able to push it beyond 1475 MHz, which is only 25 MHz more than the Boost VBIOS the card ships with. Memory had more scope for improvement with an additional 175MHz actual (700MHz effective) on our sample.
The real world impact of this extra frequency? Negligible quite frankly. The RX 580 isn't a very overclockable GPU and prospective buyers should assume there are minimal gains to be made, anything that they do achieve is a bonus.
Sapphire permits voltage increases of up to 200mv (0.2 volts) through its TriXX utility, but even applying the maximum additional voltage we weren't able to get 1500MHz stable.
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