Interesting...
I had a similar (though) opposite experience. I used Fram filters (2 one quart filters) during break in for my 427 with a HV bluprinted
oil pump and a HP bypass spring in the block.
I got 85-90 psi at speed (over 2500 rpm) and a low of 50 or so at idle. After 500 miles I went to Bosch
oil filters. I got 70 psi and 40 or so at idle. Same brand
oil, 25/50 Valvoline, same temp. It wasn't gradual... Bam it just changed.
I switched to bosch after reading a thread about Fram and some of the specs from a website that did an exhaustive analysis of the filters contents and build materials. Napa Gold (WIX) and Ford FL-1's were among the highest rated. Mobile 1 filters were rated pretty high too.
It may be Fram just has really bad quality control. I can't imagine a 30% increase or in my case decrease from using one brand to another. I'm almost ready for an oil change again. I have a pair of Moble 1 filters and was going to wait for 2500 miles on my new engine to switch to
synthetic 20/50. I'll let you know what happens then.