You are in a fortunate position to have a donor vehicle that data can be read from & as Mark has said, the answer will be in the live data shown between the two.
I'm with Fiachra where he mentioned,
>>>Look at your boost pressure @2500 RPM. I would expect to see a much higher figure like 200 KPA which would corespond to around 900mg/stroke<<<
I would also release the exhaust from turbo & see what changes, if anything.
What is the signal wire voltage from MAF at idle, 1500 & 2500 revs on donor vehicle and faulty vehicle along with the boost pressure & airflow readings at the same RPM?
>>>I am reliably informed that all turbo pipes have been checked for leaks<<<
Do you know how this was done Pete & did the checks include the intercooler, can you smoke or otherwise pressure test the intake system from turbo outlet to intake manifold ?
The only pipe that would collapse under acceleration would be the pipe from MAF/air filter to turbo inlet, all other pipes will be, or should be, positive pressurised so wont collapse but may expand, split or leak.
Regards, Tony