1) The 6000 will never be sold, unless some strange miracle happens in the next week or so.
2) The 6000 has a unified frame buffer, but the textures need to be repeated for each chip (4). so to find the actual useable memory on a 6000, you would subtract the frame buffer from 128, then divide the remaining number by 4, and add it to the frame buffer.
3) FXT1 gives an 8-to-1 compression ratio, and has very little loss in quality when the textures need to be compressed "on-the-fly". Remember that when determining how much memory it has (and needs)
4) This is all moot. The 6000, as I said, is dead. As far as how fast it is/was/would've been, it oblitered the GTS-U in DirectX games, and was significantly faster in OGL in 1024 and 1280, and marginally faster @ 1600x1200. I don't know (nor do I care) what the 800 or 640 scores were.
5) FSAA on the 6000 obviously obliterated the GTS-U.