The cardPlease head on over to here to see why we think AMD's done a good job with Radeon HD 5870.
Vapor-X cooling was first introduced by Sapphire on the Radeon HD 3870, and the principle remains the same for the HD 5870. If you want to know more, Sapphire's Bill Donnelly ran through the technical details of the system on HEXUS.tv.
Whilst the Radeon HD 5870 isn't a particularly power-thirsty card, better-than-reference cooling will help in stabilising higher frequencies. To this end, the Vapor-X - part of the aftermarket range alongside the TOXIC - clocks in at 870MHz core and 5,000MHz memory, up from the default 850MHz/4,800MHz.
The clock-speed increases aren't huge, clearly, leading us to believe that yields on the advanced 40nm process aren't fantastic. Of course, having low factory-overclocks does open up potential for the higher-clocked TOXIC card, but such are present yields that we're unlikely to see it made available.