If leaks are accurate, slightly faster (tiny bit).

well, if the graphs hold any water it's even a tiny bit faster at stock clocks (1000MHz) than a ~17% overclocked Titan X (stock 1002MHz, in graph 1179MHz), but it does look a bit weird that chiphell was able to test a cut down GM200 aswell - sure, those probably are a side product of the Titan X production anyway, but the corresponding card, the 1080Ti is likely to be released in late fall or winter

They got the 290X, Titan, Titan Z, 295x2, Titan X, and soon the 390X correct.  They always specify how true they believe a rumor to be and are fairly carefull to get multiple sources for each rumor.

Why what did they get wrong?

To understand what it means, the easiest way is to look at the 290X and the rumored specs of the 390X.

The 290X has 2816 shader units (also called Stream Processors) and 4GB of GDDR5 memory. Meanwhile, and acording to that slide and most of the past leaks, the 390X will have 4096 Stream Processors with 4 or 8GB of the new HBM, High Bandwidth Memory.

Now, the 290X, on its "Uber" configuration, performs like this: http://www.anandtech.com/bench/product/1438

So, imagine a card with 45% more stream processors and better memory that is capable to give almost 50% more performance than the 290X and you'll have the 390X.
Oh, and using roughly the same power.

Well for one thing they usually get the release dates wrong and they also wrong about other stuff too ...

LOL they specifically note that the release dates are guesses based on estimations and rumors.  However they did get thje 390X, 290X, GTX 960, and Titan X release dates right.  Do you really expect them to be 100% correct every time?  Hell even AMD doesn't know the exact dates until about a month before a product comes out.

Unless they'd favour NVidia, of course.

IF the leaks are true, then it's very likely that we'll get an air cooled version of that card.

And not only because of the name, the WCE that stands for Water Cooled Edition which kind of implies a non water cooled edition, but because the card is a 300W chip like the 290X. And if AMD's AIB partners could tame the infamous 290X with third party air coolers, they'll be able to do it with the 390X too.

I hope you know for your sake that I'm agnostic as far as it goes when it comes to chip designers ...