That means no GT. And another thing: the 256 MB that are attached to 6600 series doesn't mean that they are better 128 MB. I had an extensive search for that. In simple way: the main thing why it isn't better is because the GPU isn't quick enough to make use of the 256 MB. In other way: the 128 MB is enough for the 6600 version.
The 256 MB on the 6600 is just made for commercial purpose. Because if you add 256 MB it sounds better then 128 MB.
But I think if you buy the 6800 then it's good to have 256 MB attached to it, because the GPU of that videocard makes use of it.
I don't remember where I got that information actually. Otherwhile I would have shown the link to you.
For more reviews of videocards, you can read here:
http://www.guru3d.com/index.php?page=Videocards