The BRZ/GR86 research video that Sgt Gator provided earlier was exceptionally well done and great information. In earlier threads (St Gator?) I have seen oil pressure degradation at high RPM.
As I mentioned to Dave, that suggests G-rotor cavitation, and I feel that is exacerbated by the regulated oil being re-introduced into the oil pump feed from the pan. The G-rotor gets foamy oil under high suction, a recipe for cavitation.
A solution I have envisioned is blocking the OEM regulator discharge path and create a new path to the oil pan.
Alternatively eliminate the OEM regulator and plumb an adjustable external regulator to an existing oil galley. Plumb the external regulator discharge to the oil pan.
The end in mind is non-foamy oil exclusively to the oil pump.
jim