Exact specifications, as in the number of shader processors or clock frequencies, are still unclear. Our sources suggests that Radeon HD 5830 will use GDDR5 memory and offer performance on the line of AMD's Radeon HD 4890 card, but at a lower price.
Radeon HD 5830 with HD 4890 performance, but cheaper | NordicHardware
Finally, if this will be launched it will fill up the gap between the HD5770 and the HD5850. Appropriate for those users who can't afford the HD5850 but wants something much faster than the HD5770.