In theory, an obstructed filter should cause the filter bypass valve to open, maintaining oil pressure.

I could not agree more.

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On My year and model it has that the Bypass valve in the Oil Filter Housing opens at 3.5 bar. That is about 50.75 psi.

I am not sure what Pressure the Stock setup would show. But, I am guessing as you said it would show the same Oil Pressure if the Bypass Valve is open or if it is closed (and the Filter is not plugged).

It is not explained in the manual but that is a differential pressure between the Dirty Oil side of the Filter and the Filteres Oil side of the Filter. Meaning the Dirty Oil side has to rise 3.5 bar above the Filtered Oil side in order for the Bypass Valve to open.

I believe this means that if a Filter is starting to Plug up the Oil on the Dirty Oil side has to rise 3.5 bar above the the Filtered Oil side before the Bypass Valve is going to open.

That makes Me think that at hot idle in the face of an entirly Plugged Filter if you had a Gauge hooked up to the dirty side and the Bypass Valve opens you are going to show 3.5 bar/50.75. When in My case the Hot idle pressure is 1.5 bar/ 21.7 psi.

Also when the Bypass Valve opens you get unfilterd Oil.

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