Sapphire took it upon themselves to inject a bit of nitrous oxide into AMD's reference HD 5970 videocard, and the end result is something "Toxic." We're talking about the Sapphire HD 5970 4G Toxic Edition, which boasts twice as much RAM (4GB of GDDR5) as a standard HD 5970, as well as faster clockspeeds.
The core has been pushed to from 725MHz to 900MHz, while the memory runs at 4800MHz (effective) compared to 4000MHz on most other HD 5970 cards. According to Sapphire, this is "not only the fastest card in its class, but the fastest in the world."
To cool the added RAM and higher frequencies, Sapphire partnered with Arctic Cooling to design a wicked looking heatsink/fan assembly. Constructed of nickel plated heatpipes and fins, the cooling contraption consists of three dual-ball bearing fans Sapphire claims are low noise.
Everything else we know about the Toxic Edition is standard fare, if you can even say that about a dual-GPU videocard. What we don't know (yet) is how much it will cost and when it will ship.