Well, I did the best of both worlds on my oil filter today. I got the Mobil One (very good filter, great pressure in the 4.0L) and it's the one made for the Ford 5.0L Mustang engine. It takes another half quart of oil therefore increasing the oil capacity by that much, always good to hold more clean oil. As soon as I started it up, a few seconds later it got to pressure, and it's much higher than before. It sits at 5/8 on the gauge at cold idle and just a hair above half at warm idle. Very big improvment over the Pure One filter I took off. My pressure was crap before, now it's great!
Also, I changed both 02 sensors and just in the 30 or so miles before I filled up, I noticed an increase in mpg. I usually don't get more than 220 miles to a tank, I changed the sensors and oil at 1/8 of a tank and when I filled up with just 17.866 gallons, the usual, I had 238.8 which is an acceptable improvment over the past tanks of gas I've put through it. I can't wait to see how much I get out of this tank!