Interesting comparisons here. Much of this however is just theoretical comparisons and in the real world it's going to be tough to tell which one of the OEM pans is best.
Our "Unlimited" class 06 STi has been working well with the OEM oil pan but we also had an older 04 setup on our other car that worked perfectly also. We did notice the 06 oil pickup tube was too short and we either used one from the 04 or we just ordered another 06 pickup and it was much better.
I'm going to test the 2.0 WRX pan, pickup, etc on my current engine and I think it's going to work better than the 06 STi pan. Why? On an engine that belches out more than 600 whp it won't let you run the oil level at the full mark. It just pushes that oil out through the crankcase breathers and settles between the low and high mark on the dip stick. I would say it needs to be 1/4-1/2 quart lower than full. At this level we have never had an oil starvation issue. Now the difference between this ideal level and the low mark is about 1/2 quart and we have seen oil starvation occur at this level. If you do the math this works out to be about a 1/2 quart safety margin
. I think the 2.0 WRX oil pan with the extra 1 quart capacity is going to allow us to run the oil level so that we'll have about 1/2 quart more oil in reserve allowing a full quart buffer before oil starvation occurs.
This is my theory at least in regards to the OEM pans. I have no proof it will work better, I'm just hopeful it will be. I'm sure there are better aftermarket designs and I may run one some day.