They aren't 4.7GB, not sure where you got that number from, they are the exact size of a DVD. You may be confused because pirates likely compress.
http://wiki.redump.org/index.php?title=Redump.org
The flubber animation isn't linked to the hard drive at all, in fact it's compiled directly into the kernel. I do agree it's weird you'd see problems with 1 type of hard driver over another but it shouldn't effect the boot animation at all. Could be related to power draw?