Allow me to recap possible R600 XTX bandwidth figures, based on available Samsung GDDR4 parts (i've "rounded" them up a bit for easy reading):
R600 (512 bit bus):
- 1.0 GHz GDDR4 (x2): 128 GB/s
- 1.1 GHz GDDR4 (x2): 141 GB/s
- 1.2 GHz GDDR4 (x2): 154 GB/s
- 1.4 GHz GDDR4 (x2): 179 GB/s
Just for curiosity, here are the numbers for both the existing G80 GTX (384 bit bus), as well as if it was using the same GDDR4 chips detailed above, while keeping the same bus width.
G80 (384 bit bus):
- 0.9 GHz GDDR3 (x2): 86 GB/s (current version)
- 1.0 GHz GDDR4 (x2): 96 GB/s
- 1.1 GHz GDDR4 (x2): 106 GB/s
- 1.2 GHz GDDR4 (x2): 115 GB/s
- 1.4 GHz GDDR4 (x2): 134 GB/s
edit
Forgot to mention this, but the 1.0 GHz GDDR4 part (as used in the current X1950 XTX) is not listed anymore at the official Samsung semiconductor website, and was replaced by a 1.0 GHz GDDR3 chip.
So, GDDR4 seems to be restricted to 1.1, 1.2 and 1.4 GHz, unless someone has a pile of older GDDR4 stock in storage for PCB integration.
My personal bet would be at 1.2 GHz chips for the top R600 XTX, but i guess final decisions can be made very late, based on the number of different SKU's and RAM prices.