Yes, they need to rev to power the turbo - I understand this. Pre-crossflows don't flow air very well. You can work them until you're blue in the face, and they still don't flow air as good as a crossflow..
Clearly this engine has a big turbo, so it needs to rev that high. It's pointless, for 300hp, it could just use a more efficient smaller turbo. Phil has well over 300hp and he is only revving to just over 7000rpm.