The power of rebranding at its best, and that's not saying much
Long story short, it is, for the most part, a rebranded Devil 13 HD7990, which was launched back in August (thus, not all that long ago).
The Tahiti XT GPUs operate at a frequency of 900 MHz, while the 6 GB of GDDR5 VRAM are clocked at 1,375 MHz (5.5 GHz effective).
Coupled with the memory interface of 384 bits x2 (one for each set of 3 GB memory), that leads to a very high performance level.
And here is where the single relevant difference kicks in (not counting the looks): PowerColor's Devil 13 HD7990 is designed with a dual BIOS function, whose special switch can put the secondary BIOS in charge. The GPU speed is pushed to 1 GHz when the setting is chosen. The new PowerColor HD7990 jumps only to 925 MHz.
Moving on, the cooler is big (triple-slot), due to the three fans needed to keep in check the heat produced by two overworked GPUs and a bunch of RAM chips.
Fortunately, many high-end motherboards of today, which support CrossFireX multi-GPU setups, have the primary two PCI Express x16 slots far enough apart to still allow that capability to be used.
The multi phases design, UHB, digital PWM and PowerIRstage technologies contribute to the stability of the voltage as well, even at high loads.
Finally, PowerColor HD7990 possesses a thermal design power of 550 Watts and, for EyeFinity setups (up to six monitors used at once), an extensive set of video outputs: HDMI, Dual-Link DVI, single-link DVI and two mini DisplayPorts.