As I mentioned above, the Region 4 disc is quite different from the Region 1. The Region 1 DVD is promoted as "The Killer Cut" — it is a special edition, and a different cut from the theatrical release. The differences aren't large in terms of screen minutes, but I think it is more coherent. As for the extras, well, the Region 4 disc has none, and the Region 1 has:
There is a strange start to this R1 disc. When the disc is inserted, you get a choice of three options. As far as I can tell, this choice just controls the transition to the main menu, and the animation and music of the main menu — nothing more. The three choices are:
An interesting difference is that the R1 disc has Spanish subtitles (only), while the R4 has only English. If you need subtitles, then that difference could be important to you.
One area where the Region 1 and Region 4 are equivalent is transfer quality — both feature essentially reference quality video and audio transfers.
I strongly recommend the Region 1 disc over the Region 4 — the version of the movie is better, and it has lots of extras. Maybe the retail Region 4 version will offer the better cut and lots of extras — cross your fingers!