There's no official word on the release date, its all gone a bit quiet. And looking at the design of the boards, it seems likely its a GT with the missing cluster enabled. Overclocked, assuming it clocks the same as a GT, then a 15% increase in performance from the extra shaders. With the same limitations in frame buffer bandwidth.
Just some speculative comparisons for you.
8800 Ultra
Core Clock: 612 MHz
Shader Clock:1500 MHz
Memory Clock:2160 MHz
Memory Bandwidth: 103.68 GB/sec
Shader Operations:
192000 Operations/sec
Pixel Fill Rate: 14688 MPixels/sec
Texture Sampling Rate: 19.6 GTexels/sec
Framebuffer: 768 MB
Memory Bus: 64x6 (384 bit)
Shader Processors:128
Texture Units:32
Raster Operators:24
8800 GT
Core Clock: 600 MHz
Shader Clock: 1500 MHz
Memory Clock: 1800 MHz
Memory Bandwidth: 57.6 GB/sec
Shader Operations:
168000 Operations/sec
Pixel Fill Rate: 9600 MPixels/sec
Texture Sampling Rate: 33.6 GTexels/sec
Framebuffer:512 MB
Memory Bus Type: 64x4 (256 bit)
Shader Processors:112
Texture Units:56
Raster Operators:16
8800 Ultra XXX
Core Clock: 675 MHz
Shader Clock:1667 MHz
Memory Clock:2300 MHz
Memory Bandwidth: 110.40 GB/sec
Shader Operations:
213376 Operations/sec
Pixel Fill Rate: 16200 MPixels/sec
Texture Sampling Rate: 26.6 GTexels/sec
Framebuffer: 768 MB
Memory Bus: 64x6 (384 bit)
Shader Processors:128
Texture Units:32
Raster Operators:24
8800 GT TOP
Core Clock: 700 MHz
Shader Clock: 1750 MHz
Memory Clock: 2000 MHz
Memory Bandwidth: 64.0 GB/sec
Shader Operations:
196000 Operations/sec
Pixel Fill Rate: 11200 MPixels/sec
Texture Sampling Rate: 39.2 GTexels/sec
Framebuffer:512 MB
Memory Bus Type: 64x4 (256 bit)
Shader Processors:112
Texture Units:56
Raster Operators:16
8800 GT OC (mine
)
Core Clock: 800 MHz
Shader Clock: 2000 MHz
Memory Clock: 2200 MHz
Memory Bandwidth: 70.4 GB/sec
Shader Operations:
224000 Operations/sec
Pixel Fill Rate: 12800 MPixels/sec
Texture Sampling Rate: 44.8 GTexels/sec
Framebuffer:512 MB
Memory Bus Type: 64x4 (256 bit)
Shader Processors:112
Texture Units:56
Raster Operators:16
8800 Ultra OC (Good stock cooler)
Core Clock: 700 MHz
Shader Clock:1750 MHz
Memory Clock:2400 MHz
Memory Bandwidth: 115.20 GB/sec
Shader Operations:
224000 Operations/sec
Pixel Fill Rate: 16800 MPixels/sec
Texture Sampling Rate: 44.8 GTexels/sec
Framebuffer: 768 MB
Memory Bus: 64x6 (384 bit)
Shader Processors:128
Texture Units:32
Raster Operators:24
8800 GTS 512
Core Clock: 650 MHz
Shader Clock: 1625 MHz
Memory Clock: 1940 MHz
Memory Bandwidth: 62.08 GB/sec
Shader Operations:
208000 Operations/sec
Pixel Fill Rate: 10400 MPixels/sec
Texture Sampling Rate: 41.6 GTexels/sec
Framebuffer:512 MB
Memory Bus Type: 64x4 (256 bit)
Shader Processors:128
Texture Units:64
Raster Operators:16
8800 GTS 512 OC (Assuming same headroom)
Core Clock: 800 MHz
Shader Clock: 2000 MHz
Memory Clock: 2200 MHz
Memory Bandwidth: 70.4 GB/sec
Shader Operations:
256000 Operations/sec
Pixel Fill Rate: 12800 MPixels/sec
Texture Fill Rate: 51.2 GTexels/sec
Framebuffer:512 MB
Memory Bus Type: 64x4 (256 bit)
Shader Processors:128
Texture Units:64
Raster Operators:16
Now bear in mind what matters is shader ops and texture fill rates. Apart from the bandwidth issues at high res+AA and the frame buffer filling up with only 512Mb and render limits from the ROP count. Then the new GTS is going to be some serious Ultra competition at lower < 1920x1200 res+AA.