Your power band drop at or over 2500rpm reads similar to what I have been living with..
I have a '08 3.0d E83........
The main attribute that has affected the car is the fouling or clogging of the Diesel Particulate (second) exhaust filter under middle of the car.
I have had the DPF out twice to clean it out with hose water (I appreciate this is not a long term solution) and it makes a huge difference to the revs (over 4500 rpm) and power band.
I also have found (and replaced) the DPF temperature probe was open circuit - the ECU would not engage the regenerative burn as there was no temperature reading to inform the ECU of the right temperature conditions.
I think I still have a prominent issue of the DPF fouling with a possible oil consumption issue.....oil in the intake......and sooting up the exhaust more tha usual.......
I'm still looking into an alternative step to take for the DPF clean......