I also run FL1A's. Some filters dont well, filter as well, and as a result they produce a lower pressure delta. A more restrictive filter can show a little less pressure but can be doing a better job of filtering.
K&N or the Factory Ford Ones (Motosport) - Now before anyone starts calling me a high roller from using a K&N, let me remind you. $15 for an oil filter is fuck all when you've sunk over $15000 into an engine.
Decent, but it better to go with k&n, just changed my oil yesterday. Had mobil 1 in the gt and after 4000 miles, it was pretty black, that was using a motorcraft filter. We'll see how the k&n one does on there. Supposedly the oil looks almost the same as when it went in with this filter.