Yes, the flow would be the same until the relief pressure was hit. The pressure would be less (with thinner oils) but the flow would be the same. I think it is time to revisit my original articles of 16 or 17 years ago. When the oil is at my Florida start up temperature the pop off valve is already hit. The pressure at idle is 80 PSI. That means that at any RPM from then on, before the oil temperature gets up, the flow is the same. There is no increase in flow with increasing RPM. 'Not good in my book.