3-31-2011 news by fudzilla

HD 6790 is based on the Barts GPU, the same one that is used forn the HD 6800 series, even the PCB is similar to the one used for the Radeon HD 6870 cards. There's a max TDP of 150W and disabled shaders might even be unlockable.
The upcoming HD 6790 cards will have a great overclocking headroom, 1GHz is probably quite easily achievable.