I just discovered (extracting the music files) that Polyphony even put speech files (in Japanese AND English) of GT4 Prologue on the disc! These are the instruction files for the license tests. I think they did it to make the game look bigger than it actually is. Those *.ss2 files (about 100) should be removed to make it fit onto a DVD5 without a problem (ok, you would need a rebuilder). But when you remove those files, there is no need to downsample something else! What do you think? Why did they keep those unnecessary files?
just my 2 cents.