I'd say it's more to do with maxing-out the MAF reading, which may well then reduce the boost on the turbo to protect it. If that's the case, it'd only be worth getting if you were going to have a custom remap (and maybe uprated turbo) AFTER having it fitted.

Oh, and I'm another proponent of clean paper filters rather than anything more fancy. I do have a PD160, although it's more to stop my car turning into a sooty Red Arrow when I put my foot down than any performance reasons...

Very true on the above. Unless you intend to have a car remapped with a hybrid turbo there is no real point in fitting any larger induction kit. Fitting a panel filter of some sort will increase throttle response a bit but not add any noticeable power. A paper filter is very good and the only reason i can see for replacing it with a so called up rated panel filter is to save money on buying new paper filters but then a lot of people tend to over oil the panel filter which can kill the MAF, which is their fault not the panel filter.

A bit of interesting reading on test done on so called "up rated panel filters". LINK

Mine was about twice the size of mongrel boys though. mybe too big.

I went for the one that F1 recommended to be honest. I wondered if they'd done some testing.... It did seem as if they had a size that came suitable to all PD130 applications.

BMC airfilter and container comes in two sizes the only other differences are the connectors and piping etc for the different engine makes and car models.