I don't have it written down, but I did check the oil pressure with a gauge to see the differences with synthetic, conventional and with OE, Wix, Fram and Amsoil filters at idle and higher RPM both before the filter and after the filter.
The synthetic and Conventional had almost identical pressure before/after the filter when at full operating temperature. The Syn had only 1 psi drop in oil pressure before versus after the filter when cold. The conventional was almost 5 psi drop.
I don't remember exactly the numbers as this was almost 3 years ago but The one that had almost the same pressure entering the filter as exiting the filter was the Amsoil EAO and so I stuck with this one, Wix was only 0.5psi difference. The Fram was the worst at 3psi, and the OE was 1 psi.
This is the average PSI drop between idling and 2K rpm.
I had a spin on adapter to divert oil to an oil cooler and I spun it on, hooked up gauges to the inlet/outlet hoses (before/after filter) and measured the differences.
Hope that helps you...