I did Bergen - Moi-i-Rana last year and it was a looooooong and slow ride!
Bergen - Oslo (6 hours)
Oslo-Trondheim (6 hours)
Trondheim - Moi-i-Rana (overnight, 6 hours). That train goes onto Bodø.
Sorry I know it doesn't answer your question.. but thought you'd like to know about it all ..!
I wish I have the time and patience to do that trip again..