Although the performance of AMD's Fury X hasn't been quite as impressive as a lot of people had hoped it would be, the fact that it comes equipped at stock with a bespoke water cooling solution, should suggest that it has plenty of overclocking head room. Unfortunately though, getting anything more than a single digit percent bump to the core clock is proving almost impossible to those that try.
Although some publications have been able to increase the clock by around 10 percent, tweakers at MaximumPC barely managed 7 percent, which resulted in around a 5 percent improvement in real-world performance. However, as much as they'd like to go after AMD for this, especially since the card's temperatures are still quite low at those speeds, they blame the lack of supporting tools for the low headroom.
As it stands, there is no ability to increase the core voltage of the R9 Fury X, which traditionally gives a lot more room for increasing core frequencies, at the expense of temperature. Since the water cooling allows for such low load temperatures however, it may be possible to overclock the card much further when the ability to tweak its voltages becomes available.
This isn't just something AMD should be hoping for though, but something it needs. While we saw that when paired at ridiculous resolutions, that the Fury X cards are very impressive, they still fall behind the 980 Ti from Nvidia at more traditional settings. Similarly so, that card is already coming pre-overclocked by large margins from partner companies, so it's only getting more powerful as time goes on.
Of course, your results with overclocking the Fury X may vary, since nothing is guaranteed when it can be so dependent on which batch your card came from and its chip's own particular quirks.