JQP,
Quite a few movies takes less than 4.7 gb, after ripping out the 4:3 version, foreign soundtracks, menus etc.
If you are happy with just the movie, probably you can get all of it on a disc, without recompressing video, 50 percent of the time.
Not sure about DVD xcopy, but there is a freeware util called DVD Shrink, that has a neat feature. It can compress key frames (I think..) (an Mpeg2 stream consists of different kinds of frames. Some frames are the entire image, like a jpeg picture, while most only show the difference from the last frame - to save space)
Using that, you can take the quality down somewhat, in increments (90% quality, 75% quality etc), without having to completely redo the movie. It takes about half an hour on a fairly slow computer.
On your other issue, yes there are 9.4 GB flipper discs, but only for DVD RAM, which is a rewritable format that seems to be loosing out to DVD+RW and DVD-RW. It is actually the best format of all of them when it comes to storing data, as the recording technique is very much like how a harddrive works. The discs are expensive though.