Price/performance beast right there.
Even at RX 480 levels, the 4GB vRam doesn't seem to give that card any penalty.
http://www.legitreviews.com/amd-radeon-rx-480-4gb-versus-radeon-rx-480-8gb_183576/6
A few % drop at 4k, but not the intended resolution of that card anyhow.
The 4 GB Rx 480s are going for $200 OR LESS on the Egg. Paying $280 for an RX 580 is silly. Flash one like yours to an RX 580 and it will be at the top of the price/ performance chart alongside the Rx 470.
I'm already overclocking my card to the max it can do. I was interested in the RX580 bios because it might have allowed higher voltages and power limits (although the Sapphire Nitro power limit is already pretty high and doesn't throttle unless overclocked quite a bit) without requiring a modded, unsigned bios (which can bring some problems, like for example inability to use hardware video acceleration) or to apply a voltage offset using Afterburner, Trixx or similar programs (which is not very reliable and increases idle voltage too).
There is a third party utility called WattTool which previously allowed to increase core voltage beyond 1175 mV using the Wattman API, but starting from drivers 17.4.1 AMD introduced some limitations/checks, and the VID now cannot be higher than 1175 mV anymore, at least on the RX480.
The newer BIOS in addition to idle state improvements and higher core voltages perhaps also have better memory timings, which require a custom, unsigned bios to use on the RX480.
I've already flashed my card many times for many tests with custom BIOS, and "bricked" it a few times with some of the wackier tests. Unless the card gets physically damaged such a bricked state can be easily recovered, especially with a dual BIOS.