I don't know where they got it from, but in Donanimhaber it says that ForceWare 177.40 Beta has a "GT200-400" tag in it, along with GT200-100 (GTX 260) and GT200-300 (GTX 280).

This is probably the 55nm GT200. I think it shouldn't be too far away now since NVidia has already began producing in 55nm (9800GTX+)