Following debate on Saabscene, it seems likely that my car isn’t producing as much power as I thought it was.
The thread here contains more info. It looks like the dyno figures may well have been adjusted to flywheel rather than being wheel measurements.
This matches my peak torque at 1.4 bar boost to similar flywheel figures from equally modified Saabs, and a peak power of 243bhp would be about right with the 0.75 bar boost at 6000rpm.
This of course leaves me with a problem – I am not getting full boost through the rev-range, leaving me with reduced power. Hopefully a solution will be found…