Radeon R9 280X MSI Gaming 6GB Edition is a special edition of the high-end Radeon R9 280X.
This edition comes with a custom cooling system called "Twin Frozr", which reduces the card's temperature under load, significantly and comes overclocked out of the box in the central unit that was increased from 850MHz to 1000MHz, while the Boost clock is now of 1050MHz.
Furthermore, the frame buffer was doubled to 6GB which will only prove very slightly useful since the card itself is not powerful enough to work in circumstances in which that much video memory is required and thus become the bottleneck itself.
Benchmarks indicate a modest 4% performance boost over the standard edition.