There are quite a few tests around that give similar overall results. I think everybody would agree that the best filter for stopping dust getting in the engine is the standard one. Any performance filter oiled cotton or foam has larger openings in the filter medium that allow more dirt through.
OE filters will cause more pressure drop than a performance filter like a K and N filter. Although some OE filter set ups are pretty good.
When I had my Passat PD130 on the dyno it was running just under 200bhp when we were mapping it with a hybrid turbo. In an attempt to get it to 200bhp I removed the standard Mann PD130 air filter and the car made just over 1bhp more and about 3Lb/ft of torque. That was a standard air filter that had done over 10 K miles against no air filter at all.
When I changed the air filter for a new one I unfolded the old one.
The air filter unfolds to 28 feet long, that is a lot of surface area and the reason the standard one is so good.
So to me fitting a performance air filter on the likes of a standard car or even a slightly modified one is mostly a waste of time. The standard air filters these days are good.
A similar thing found here with a Leon TDI being tuned, the standard air filter was removed and it made no difference to the power of the standard 150bhp engine.
There is an air filter test on several performance filters here.
http://www.fastcar.co.uk/2012/05/04/performance-car-air-filter-test/
From those test results "It was also worth noting the most restrictive cone filter we tested had a pressure of 1.21kPa at 6.0m3/min, whereas the best flowing filter within the standard airbox was 2.56kPa."
To put that in perspective 1.21kpa is 0.18 psi and 2.56 kpa is 0.37 psi .
If you have a seriously modified car and want the maximum air then a large cone filter with no air box, lots of cold air feed and some way of stopping hot air from the engine being pulled in is the best to get maximum airflow, however the filtration isn't as good as OE but most of these kinds of engine set ups aren't likely to do 20K miles a year.
Oiled filters can cause issues with MAF's especially if they are over oiled.And nearly all the performance filters are oiled.
Karl