I recently got a 4k monitor, so I'd just like to tell you about my experience with it and gaming.
But first, for productivity it is amazing. I have it at 100% scaling, it's a 28", so the text is comfortable for me to read at my usual distance of ~50cm, however any further and it becomes uncomfortable to read on. I think that 32" would be the sweet spot in terms of readability of text and whatnot.
Anyways, I have an R9 290 @ 1100Mhz, which is by no means slow, however @ 4k, it struggles to give me a playable framerate in BF4, Tomb Raider and Bioshock Infinite. Older games seem to do well, as does Dota 2 and pretty much all Source games. In reality, 4k really is the realm of multiple GPU's at the moment, if you are a graphics whore, like myself.
Edit: As a side note, if you use 100% dpi, then you need a high dpi mouse, since it has a lot further to traverse, this was something I didn't consider when buying it, it made my 800dpi mouse completely useless.
You can turn down AA because the ppi is higher, so 2X is fine and maybe you need 4x. I agree with you, cards aren't as good for 4k but later down the road when 4k slowly takes place of 1440p monitors it'll follow the same pattern that we see today.
On BF4 I don't run AA, it just thrashes the performance too much, on Tomb Raider and others I run 2xAA since that is all that seems necessary to completely ditch jaggies at that resolution.
My friend has a 1440p monitor and to be honest if you have one, 4k probably isn't a worthwhile upgrade, especially not for gaming. If you read tones of code though and are space limited so a portrait monitor is out of the question, 4k really does make things easier. But I think everyone should look at 4k as a case by case kinda thing, given the expense involved.
Question, Can the human eye even discern a difference between 1080P and 720P on a standard 17-24 in monitor? wouldn't 4K be for something that only multiple monitors, or one massive screen benefit from? I understand wanting big pictures at good frame rates, but how big of a screen does one need before the market is like "he, we have 9k TVs!" and people are like "whatever, I can already see the hair in megan fox's nose,...from space. need nothing larger."
Like you said, you need SLI or Crossfire to drive 4K 60 FPS gaming at the moment. A single R9 290 is not enough unfortunately. Hopefully the next generation of graphics cards will enable 4K gaming for the average PC gamer.
My main purpose was for coding, I can fit two seperate code windows, the debugger, the logger all on the screen at the same time, more if I really want to squeeze. That was my reasoning for getting it, with gaming been a secondary thought, which is why I went with a 60hz monitor.
By the way, don't get the 30hz 4k screens with the intention of gaming, it is terrible. My screen has 30Hz over HDMI, so I tried it out to see the difference and it really is night and day.
I'd definately need a second 290 for watchdogs if it is all it is supposed to be on release.
@ProSonicLive I have only watched one 4k video on it and I really couldn't tell the difference between that and 1080p. I really don't think 4k for media is such a good idea at all.
In workspace? Yes. In video? Yes, but somewhat less so. In games? most definitely.
On a phone? Sure, but the difference isn't quite as big...
On a sidenote... I hate how they switched from vertical to horizontal with the naming of 4k, very irritating, stupid, and pointless. Just like those idiots that thought it'd be a great idea to express kilobytes (and up) in 1000s instead of 1024s, it's just wrong.
The average PC gamer will still be on 1080p with the next generation of graphics cards. And the one after that, and probably still by the one after that. By then we're about 3 or 4 years further and who knows. But next year? Hell noes.