1750MHz is standard for the 4GB version of the RX 480/580... it can be clocked to 2000MHz (up to a Max of 2250MHz) quite comfortably., although I wouldn't recommend it if you game for long sessions.
Although it's definitely unusual it's using Elpida Memory instead of SK Hynix.
Still beyond that, see nothing wrong.
Now as a keynote... that video you linked for CS:GO Performance does nothing but showcase how little that individual actually knows about AMD Hardware and Settings. DO NOT Follow his Recommendations for better Performance., not that you should care given absolutely maxed out you should still be getting 120FPS+ at 4K on an RX 580., the game isn't very demanding.
As a note the "Out-of-the-Box" Settings are already Optimal for Gaming, with the exception of the Texture Filtering which can add some minor performance (it doesn't add Performance Stability... that's simply bollocks. The difference between the Filtering is Quality = Quadratic, Standard = Anisotropic and Performance = Bicubic... the performance difference is between 1-5% but is Game Dependant).
Beyond that, you want to disable the AMD Shader Cache on Games that have Shader Cache Optimisation (i.e. Elite Dangerous, Infinite Warfare, etc.) as the AMD Optimised is a less Optimal in said Scenarios. You want to set Tessellation to x8 instead of AMD Optimised or Native but this only has an effect on Games that heavily use Tessellation (i.e. Crysis, Alien Vs. Predator, The Witcher 2 / 3, etc.) ... or hell anything with NVIDIA Gameworks.
Beyond that FTRC / Chill / Efficiency disabled is a useful. I'd also go to Global Settings / Wattman., change Power to +50% ... this will improve Frame Stability as it'll typically keep the Peak Boost Clock better. You can also achieve this by lowing the Voltage for each P-State Clock, but this is a bit more Trial-and-Error.
The Default of 1150mV is what you need for 1400 - 1500MHz... you'd be better using 1080mV for 1300MHz or Lower as this will basically allow it to lock that Clock comfortably; more over it will lower overall GPU Draw from 145w Peak down to about 115w Peak; and run Cooler so, you Fan won't be as obnoxiously Loud.
Something that I'm sure the others with the ASUS Dual will attest is frankly ridiculously loud under-load (not that far off the Reference Cooler)
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As for the Synthetic Benchmark Performance... first and foremost WHAT Synthetics are you running?
But still, if the issue is entirely with the Synthetics; then what does it matter if the score is low? If the issue is exclusively there, but not in Games then you have no problem.
Still you can use the ReLive Performance OSD or a 3rd Party (Afterburner for example) to keep an eye on your GPU Clock during Benchmarks., chances are it isn't pushing the Maximum Clocks for some reason. I've seen this behaviour in 3D Mark a few times over the years, where it'll stick at Reference / Idle Clocks rather than Performance Clocks.
