If you got Petter,Seb and Marcus together, give them the same car on a 40km gravel stage with 2 or 3 stage recces allowed.IN MY OPINION Petter would be the winner.BUT he is not consistent enough during a season,so i would put Seb and Marcus ahead of him in championship terms.
Petter will hopefully have the car next year to challenge them.If i was Subaru i would not bother testing or developing this car any further,but invest as much money from this years budget in to next years brand new Impreza.