Price/performance beast right there.Hopefully a Sapphire RX580 Nitro+ 4GB BIOS will be uploaded at some point so that I can test this on my card.
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.