The OEM version is 12.4". The retail is 9.5".

Quote Originally Posted by VR-Zone
VR-Zone has learned about some new details on 80nm R600 today and there will be 2 SKUs at launch; XTX and XT. There will be 2 versions of R600XTX; one is for OEM/SI and the other for retail. Both feature 1GB DDR4 memories on board but the OEM version is 12.4" long to be exact and the retail is 9.5" long. The above picture shows a 12.4" OEM version. The power consumption of the card is huge at 270W for 12" version and 240W for 9.5" version. As for R600XT, it will have 512MB of GDDR3 memories onboard, 9.5" long and consumes 240W of power. Lastly, there is a cheaper R600XL SKU to be launched at a later date.
IIRC the R600 retail version isn't any bigger than the current 8800 series cards.