We know the Top Gear track is in GT5, it was announced a long time ago matey. If you take a look around, particulalry in the master car list thread and do a search for the track list thread and it will give you an quick glimpse at what we aregenerally already aware of or not for this kind of thing.
The main bit about Stelvio pass is just speculation, we've gone over it here. It could well be Stelvio, I'd like it to be, but we don't really know yet.