I've got a Cally Turbo with P3, it was already fitted when I bought the car.
I just tested all 5 of the powerwheel positions and got the following results. I tested them all on the same bit of road in the same gears, once.
position 1 = 14psi
2 = 16psi
I thought that position 1 would have been lower, something along the lines of standard.
I have a spa digital boost gauge that stores the peaks reached, so they should have been measured properly. The gauge stored 23psi in the last 2 days at some point.
I think I'll leave it on position one for everyday stuff in an attempt at relative fuel economy and reliability! Just spent £37.50 on 235 miles. Would have been a tenner cheaper in the Nova!