1) Xbox review copy, not 100% final.
2) Yes, you can also use your own soundtrack
3) Yes, I just can't see how anyone could stand listening to that moron for more than 5 minutes. I heard he's bad in english, but in french I'd rather play without sound at all than listen to this "Starman" guy.
4) It's totally like Burnout 2, perhaps a bit easier because you can "grind" the tracks border without losing much speed.
5) Can't tell. I sincerely doubt it could be playable on 56k.
6) Nope, but I only played for a few hours. I doubt there will be any slowdown.
I'm waiting for the final version to play the game more, I don't have much free time and since I'm quite sure the savegame from the review copy won't be usable in the final game I don't want to have to replay the whole thing.