AyyItsJay :
RX480 with 580 bios here, GTA 5 on ultra setttings + 4k res gives me stable 40fps in most areas, and 60fps in places without cars etc. It's a great GPU. Also I have the 8GB model. You can also really easily OC it and get maybe even 50fps stable. On Asus website this GPU is advertised as 4k Gaming GPU, and it works great with 4k games. Even the heavy ones. Don't listen to nGreedia fanboys. I used many Nvidia cards and couple of AMDs and I can say that Nvidia is great, but when it comes to price/performance, AMD kills it. If in Your country 1070 costs less or same as RX480/580 then go for 1070, but if it costs more then get RX480/580 and You won't be dissapointed.
So in ONE game you are able to get 40fps in 4k? That is not acceptable frame rates for most people. If you cannot get at least 60fps on ultra settings then why bother? Your lame attempt at giving an insult to those that prefer to have the best, and right now that is the nVidia 1080ti, (please note the spelling here), is just pathetic. Your argument using price to performance is what people use to justifying their purchase of 2nd or 3rd rate product just based on price and not the best performance.
This may come as a shock to you but there are many out there that will pay the price to have the best regardless of the name on the box. Right now today AMD has nothing to compete with the 1080ti in pure performance. The RX580 is a good card for 2K use but it is not a good card for 4K.
Here is a piece of advise, grow up and act like an adult and stop trying to berate those who do not make purchase decisions as you do.
(/rant mode off)