A couple of HD 6900 Series presentation slides made it out. The HD 6970 will come with 32ROPs, 96TMUs, 1920SPs @ 890MHz and 2GB of GDDR5 videomemory on a 256-bit memory interface clocked at 5GHz effective. Most importantly AMD seems to doubled the geometry throughput in the Cayman chips accompanied with some of the tessellation engine enhancements introduced in Barts would give a considerable boost in heavy tessellation scenarios. The HD 6990 (Antilles) comes with two Cayman chips onboard totaling in 64ROPs, 192TMUs, 3840SPs running at a 775MHz and a whopping 4GB of GDDR5 videomemory clocked at 4.8GHz. Idle board power is a measly 30W however the maximum TDP is 300W just fitting in the PCI-SIG high performance power envelope.
Update: Added a couple of more slides. New slides reveal active power-management to enforce the desired TDP and a new MSAA method called EQAA (Enhanced-Quality Anti-Aliasing) which is quite similar to nVIDIAs CSAA (Coverage Sample Anti-Aliasing) in terms that it uses extra coverage samples too for better AA quality while memory foot-print remains about the same.