No way, get real. 600mm^2 is not going to happen. The 8800GTX was about as big as it gets (about 480mm^2, I think).
Imagine the power consumption of a 600mm^2 die made at 65nm?!? I do not know if even 2x 8-pin PCI-E power connectors would be enough to power up this card (heck, Nvidia might have to put 3x 8-pin connectors)!
That is why I do not think it would be any more than 500mm^2, even if Nvidia cannot get it made at 55nm yet. Also, it would not make sense for Nvidia to do it at 65nm if 55nm is now already available and useful for saving costs, heat, and power consumption, and more...