Some more testing tonight has revealed that the problem doesn't seem to be dependent on throttle position, rather RPM... :Oops:
As my car is auto, at low speeds, going full throttle results in the auto kicking down and the revs jumping to 5000 or so pretty quick, and the overboost problem occuring immediately... Tonight I had the chance to put the car under heavy load / full throttle whilst keeping it in 3rd gear (read high speeds :headspin: )...
Full throttle at anything below 4500 RPM and the boost stays solid at 5psi (bear in mind that the auto 33 actuators have a lower pressure rating than the manual ones)... After 4500 RPM, the boost just rises, and rises, until I chicken out... I'd be content with a little bit of creep up high in the revs, but by 6000 RPM, it's at 11psi+ and still rising awfully fast...
Thanks for all the advice so far guys... Much appreciated... Keep it up!