Does the version on GOG use the DVD-ROM version's assets? It bundled higher resolution artwork and higher quality videos. I'd say from the download size that you're probably not using that version, as I have an ISO I ripped from my brother's bundle copy of the DVD, which comes out to 3.1GB compressed, or just over 4GB unpacked.

I can supply an image of the disc to GOG if one is needed, which I backed up from a copy my brother got bundled with his original HP desktop machine. I also assembled an Inno Setup installer which can install the full game from that disc, since the bundled installer is some 16 bit piece of crap from ancient days.

Yes the version on GOG is the DVD version : )