a turbo 4 banger might pull boost at cruise but a BB will not. I had many many highway and cruise miles on my old S/C'd 440. It never pushed any boost at speed. With vacuum readings of 20+ how can it? It would go into boost until vacuum was near 0.
Will all depend on how the turbos are sized.
We are talking turbos, NOT superchargers as you have indicated in your post.
