Ended up fixing it by changing the Rail Pressure Control valve (DRV) that lives at the end of the common fuel rail. Opposite end to the fuel pressure sensor. One end is the valve, the other is the fuel pressure sensor - make sure you get the right one. No recalibration or coding was needed after changing it.
As of writing this, it has been around 30000 miles ago and 2 years since it's been changed. It's been fine since then.
This helped a lot in diagnosing the problem: [ Ссылка ]
No EML is on when it had this problem. Basically caused by the valve sticking at certain positions and then it drives it harder till it unsticks. Then it rapidly hits the limits. Hence why the revs jumping around and very unstable.

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