I routinely put a feature film with an AC-3 5.1 track at 448kbps on a DVD-5 -- -- as Adywan did with his ESB restoration -- with no significant detriment to the video (compared to using 2.0 at 192 bps).

Could you maybe make an AC3 with PAL speedup and the same bitrate you'd be using and up it somewhere for me, so I can use it too, it would be nice to have a higher bitrate audio than the GOUT and to have the same audio on both PAL and NTSC versions.

That's easily done, so yes to both! :-)