AMD is launching their Radeon RX 580 graphics card soon, alongside the RX 570/560/550, with the entire RX 500 series being a rebranded and tweaked RX 400 series. The flagship Radeon RX 580 has already been overclocked, hitting 1.5GHz on the GPU under water.
The overclocked RX 580 in question is from XFX, with it rocking a single 8-pin PCIe connector and stock GPU clocks of 1360MHz. This means the results from this card should line up with the RX 480 clocked at the same GPU speeds, but the thing that concerns me the most is that the XFX Radeon RX 580 needed to be cooled with water cooling to hit 1.5GHz?
I can tell you that I'm hitting that on stock cooling without much tweaking. My results will be arriving very soon! :)