[aerohead]

I took baby-food container samples of a half-dozen motor oils,from Honda's 0 wt-20,to 5wt-30,10wt-30,10-40,etc.,and placed them overnight in my freezer ,at 0-degrees F.
Next morning I pulled them all and did a 'tip'-test,turning all of them over simultaneously.
All of them essentially poured out within the jars at an equal rate.
From that observation I would deduce that the cold pumpability at the filter media is not a real issue for us.
Your pressure bypass may exist to 'maintain' oil pressure within the lubrication system,modulating between cold and hot conditions,and as the engine rpm( and pump rpm) varies from idle,up to redline.