"The Sapphire HD4850 Dual Slot is a slightly different animal than the standard HD4850 from Sapphire. It maintains the same GPU (RV770) and amount of memory (512MB GDDR3 on a 256 bit bus), but is built on a Sapphire designed and built PCB, rather than using the reference design PCB. In addition to the non-reference PCB, there is the non-reference cooling solution to go with the board. There are no memory heatsinks used, but there is one additional heatsink at the front of the PCB. The clock speeds stay right at the factory specified 625MHz on the GPU core and 993MHz on the 512MB of memory. The card is slightly shorter than the standard PCB so this should allow some additional clearance in tight cases."
FULL STORY @ OVERCLOCKERSCLUB (http://www.overclockersclub.com/reviews/sapphire_hd4850_dual/)