That photo looks a lot more realistic

That would suggest at a baseline, Cayman is:

2GB frame buffer
1920 SP's
1550Mtri/s (775mhz x 2)
32 ROPs (32 pixels/clock)
3 TFlops (750 GFLops DP)

But given power constraints, Cayman XT is almost certainly clocked higher... so that should give a good idea what Cayman will be packing