It all depnds on what type of mem chips are on the 4200, I doubt we'll be lucky enough to get the same chips as a Ti4600, but maybe a 4400, in which case you could just flash your Ti4200 to a Ti4400 pretty easy. As far as core overclock go's, nVidia may be throwing the chips that cant make it to 4400 and 4600 speeds, so we'll just have to wait and see.