Now some more from BSN with supposed specs for Tahiti. They also say VLIW-5 will still be used, even though Trinity is said to be switching to VLIW-4, so one would have assumed the low end would have been VLIW-4 to crossfire with it. 7800 series is supposedly a shrinked 6900 with adjusted clock speeds, so VLIW-4 based. GCN is where things look exciting though and this will be reserved for the 7900 series for now.
So London next week is a "Tech demo", with the launch supposedly at CES in Vegas come Mid January.
The specs they give for Tahiti XT and Pro (7970 and 7950) are very juicy if to be believed:
AMD kept the unified clock concept and given that Radeon HD 7970 is based on fully configured "Tahiti XT" GPU, 2048 cores (32 Compute Units) operate at 1GHz clock. 3GB of GDDR5 memory operates in Quad Data Rate mode i.e. 1.37GHz ODR ("effective 5.5GHz"). This results with record video memory bandwidth for a single GPU - 264GB/s.
The HD7950 is based on "Tahiti Pro" and packs 30 Compute Units for 1920 cores operating at 900MHz. The number of ROPs decreased to 60, while Texture units naturally reduced to 120 (as every CU connects to 2 ROPs and 4 TMUs). Our sources did not disclose if the memory controller is still 384-bit or a 256-bit one, but the memory clock was decreased to 1.25GHz, i.e. the same clock as previous gen models. Should 384-bit controller stay, the clock should be good for 240GB/s of bandwidth.
Both products are expected to be released on CES 2012 in Las Vegas, NV, occupying the $349-449 price bracket. Those additional gigabytes of memory (and processing cores) will certainly cost a lot of $$$.
So we're looking at the very least something along the lines of 3GB GTX 580 level with faster memory. GCN is yet to prove itself but you would expect at least 25-50% faster than GTX580 3GB. I'm going to say 50-75% myself. Of course these specs are far from confirmed!
EDIT: Oh yes, and New Zealand (7990, dual Tahiti) is expected in March.