Reached 7,000 miles on the WRX yesterday and converted to synthetic motor oil- Mobil1 5W/30. I also started using NAPA Gold (#1334) oil filters, as there's a store right down the street from my house. Upon installing the new filter, I noticed it's larger than the original filter (I still had the factory one for reference) although the rubber o-ring is the same diameter. The good part was the engine now takes exactly 5 quarts of oil- put the entire 5 quart bottle in and it was right on the full mark.
I had good luck with the NAPA filters on my last car- anyone have experience with them? I searched the forums but didn't see much.