WOW...8GB of vRAM totally getting two of these to replace my 3 780ti.
Should be more than enough to max anything at 4k.

Uhh, no they don't at least not for the rumors or other bullcrap they throw at their readers ... 

There's a reason why no tech community takes them seriously ...

If accurate, how would this stack up against nvidia's Titan X?

If the rumors are true they'd be about even in terms of performance ...

I really hope it will be less of an hothead than the 290 series. If the card is as fast as the rumors suggest and they managed to bring down the powerconsumption a bit i will be impressed.

if rumors are acurate the 390X has a peak consumption of 300W like the 290X, but 40-50% better performance (especially in high resolutions)

it's pretty certain AMD will offer a water cooled version (rumored for month), which probably still will retail for 30-40% less than it's competitor, the Titan X

Well apparentally they're coming with AMD's custom water cooler.I've used it before on the 295x2 and it is really efficient, the card never went above 65° and its a two gpu card.

I would suppose this card is even cooler since the chip should be more efficient and is also one gpu only.It is a pain to have multiple cards with this cooler though.

I read the story 2 days ago over at videocardz.

http://videocardz.com/55124/amd-radeon-r9-390x-wce-could-this-be-real

I don't know how reliable the site is, but the author of the article said that unlike most (fake) leaks this one came as a pdf because it was part of an "in-house" presentation called ‘2015 Future of Radeon’ for AIB partners, and in the comments he also adds this

Well I was told more details, but I'm not allowed to share them.
I feel it was enough to post this. It's much more you'd expect from typical 'Asian' leak anyway. Take it as it is, or ignore it.

We'll see how acurate this is at Computex, in June.

What does any of this actually mean?

The thing is 4k is a huge resolution.

So memory bandwidth and memory size can matter ALOT for it.

I think if your planning on going 4k, AMD wins this round by default, simply because they are useing a new memory technology.

While Nvidia are stuck on GDDR5, for abit longer still.