what i said is pretty much 'the standard' for XviD. (if you know what i mean )
because if you go to much higher than that in file sizes, your better off just using standard DVD... because the whole point in XviD is to keep quality reasonably close to DVD at a much smaller file size... which is pretty much what i was saying.
even if you prefer 1400MB (or so) for each film... you should still AT LEAST be able to fit 3 films per DVD recordable.
and there's no real point in using XviD for large files (it sorta defeats the purpose of XviD)... if you want high quality, i would switch over to HD stuff (i.e. x264 etc)
because if i was doing 2GB (or so) per movie in XviD format ... i would rather just have the film on a standard DVD format (4.7GB Recordable) in my opinion (especially as you said DVD's are pretty cheap nowadays ) because you aint really increasing efficiency to much at 4.7GB (i.e. standard dvd format) vs 2GB (or so) (XviD format).... because following the 700MB-1400MB stuff you maximize your hard drive space and milk those 30 bucks or so for 100 discs for everything it's worth
and also... 128kpbs MP3 aint the greatest but if your trying to keep file size fairly small per film without killing image quality that's pretty much your only option is to cut the audio back in bit rate.... because i think it's safe to assume 'most people' would rather sacrifice audio quality over picture quality in cases where 700MB XviD is used.... you might even be able to do 192kbps for audio but i would probably not recommend more than that for sure if using 700MB.
but main reason i said 128kbps audio (in a 700MB file)... is because if you got a film that's around 1 hour and 40minutes or so... if you used the 384 (or 448 i think it is in some cases) bit rate .ac3 audio track that would pretty much kill image quality (like pretty noticeable with artifacts etc) on a 700MB XviD file.... which is why i recommend 128kbps for movies around 1hour 30-40min or so.
but i guess everyone's opinions can vary depending on how picky they are with image quality and audio quality etc.... but the way i see it is what i was saying for general advice is a pretty safe bet for XviD... because if your concerned with 'top notch' audio/video quality your better off just sticking to standard DVD format. (or switching to HD ) ... but i think what i was saying would satisfy 'most people'. (assuming your willing to accept 'some' image quality loss which is natural when using XviD)
just some thoughts (no offense intended)