The leaked slides claim the R9 390X has 4096 stream processors and up to 8GB HBM memory resulting in a raw computing performance of 8.6 teraFLOPS, something even Titan X will be unable to reach. The card reportedly has a core clockspeed of up to 1050MHz, a memory frequency of 7GHz and power connectors in a 6-pin plus 8-pin or 2x 8-pin configuration.
The Radeon R9 390X WCE appears to be a special enthusiast-class card that will be sold alongside the reglar Radeon R9 390X cards but at present it's unknown what's the difference between these cards other than the cooling solution.
Some performance figures were also provided by the leaker. The chart below claims that in 4K UHD gaming, the 390X delivers 50 to 65% more performance than a Radeon R9 290X.