You could actually check this in the FPGA editor, but no. There's no difference in the internals. However you don't necessarily get the same IOBs bonded out. i.e. just because a certain IOB (using the X Y location) is bonded out in the smaller package doesn't mean it will also bond out in the larger one. In addition, the ID code for the two devices will be different, so you couldn't just program one using a bitstream from the other.