Depends on your driving style....
If you are good at backsiding the jumps, smooth landings, etc, then stick with the setup as 071crazy said 40/#54 pistons up front and 25/#56 pistons.
Not so good at those, then go 37.5/#55 pistons in front and 27.5/#56 pistons in back as it will help the car settle on the not so good landings.