I've been busy lately but I managed to replace the fuel lines and the FPR. Total list of mods:
-AEM FPR
-AN8 fuel line from the tank to engine bay
-Kinugawa fuel rails, AN6, parallel configuration
-AN8 fuel filter

There is no more any pressure drop. Biggest change I've recorded is about 8 kPa but that's only during high transients, no FPR can keep the pressure exactly at the set value.

-Timo