It's definitely better to let the pitch shift upwards along with the audio speedup for PAL, rather than using anything to keep it the same. I really don't like the way this sounds, but unfortunately it's vastly preferable in sound quality, because short of having access to some real high grade professional equipment, nothing that keeps the pitch the same during speedup is going to sound any good. (And maybe not even then.) It's basically the equivalent of letting a tape reel spin faster during playback, instead of doing all kinds of complicated and destructive alteration.

I use a Mac, but I don't actually know of anything that will change the speed on the file directly. What I would do is split the AC3 into its individual channels using either a52decX or Mpeg Streamclip, then open them in your audio editor and tell it to speed them up by the appropriate amount: 25fps / (24/1.001) = 1.0427083333333..., so just over 4.27% speedup. Then you can edit the faster versions to synch as needed.