I wasn't running a restrictor, but the GT28 series RB's have a built in restrictor in the core already. I have spoken to a few Turbo places ref sourcing new core's and the restrictors and they have all said not to use a restrictor. My New turbo oil line has been setup to run no restrictor but I am currently looking for a filter to go inline.
The reason I have replaced my oil line and all the adaptor's is that on close inspection after all my faults it had a couple of bad kinks in it and undoing one of the adaptors it had a some sealant or something on it's thread (I assume a past bodge by someone to stop a leak), and I wondered if the pipe is internally damaged or any of the sealant had perished overtime and got stuck in the core causing a restriction on higher flow visually I can't see any blockages in the built in restrictor and the pipe seemed to flow perfect but something might have gone through it and blocked internally so for peace of mind I renewed it all.
Seeing as the Pressure sensor is just before this feed and oil pressure was perfect even after the turbo failed.