My 550cc sards are at 90% (no FP reg). I have very similar setup to Paul. HKS3040, HKS manifold, Arias Pistons, Stronger rods, Ported head, 256/9 Tomei cams, Trust/Greddy plenum, Q45 Thtl Bdy, Kings bearings, Redline Oil, oil cooler, Bosche pump, Big Bar & Plate cooler, 90 mm exhaust, Power FC, 21 PSI e-boost (more boost doesn't make a difference). Maybe I have hit the limit for the compressor ?