Shouldn't be that much different from the 3870 to the 4870, all there is a larger die, pcb should be very similar since there aren't any big architectural changes and the memory bus is the same

As for the gt200, well no one's quite sure because there aren't any firm rumors out yet, but if the 512bit memory is true (which it may due to how powerful its supposed to be) then it could end up being quite large. The die for one will be huge and will require a very high quality power supply, I wouldn't be surprised if its longer than the 8800ultra.

And for the r700, that's a hard one to say because the positioning of the chips and xfire bridge could make a very substantial difference in length (just look at the gddr4 and gddr3 3870x2 pictures, at least an inch difference). But I'd be willing to bet around the same size of the 3870x2 gddr3 since the rv770 dies are a bit larger and its supposed to have 1gb memory per gpu