I mean what size hose is actually connected to the water inlets of the headers ?

I agree with your thinking as far as the water flow to exhaust not changing.

What i am thinking, is if your actual line size feeding the headers is a restriction, say they are -10 or -12, by going to a larger diameter line, may reduce pressure to the point you dont even need the psi relief. You gain flow, and reduce psi at same time.

My buddy had high water psi. He had -12 lines feeding his exhaust. He switched over to -16, psi went down, exhaust ran cooler.

oh, i thought you were referring to my crossover bypass line that goes to the top of my thermostat housing. i have 1" hoses coming out of my housing that feed each header. my primary concern with switching my water dump from the block drain to the intake was the thought that some how the flow would be altered hindering my exhaust of the same amount of water as its current set up bleeding from the block drain. it seems that the flow of water to my exhaust would not be greater or less than its current set up bleeding from the block drain. Does that sound like a rational theory?? If so,, I think i will just put the dump at the intake and eliminate the dump at the block drain as its better to dump from the top than the bottom.

FWIW- I have -12 from my block adapter to the manifolds and the tails show no signs of overheating.

The flow is more critical with headers imo. I know my stellings can get pretty warm at idle speed. Wish they made different size sea pump pulleys. Im running an aftermarket 3v accessory pulley for the accessory belts. Its underdriving the sea pump. Might not sound like much but at 700rpm engine speed, the pump is only turning like 500rpm or something like that, where a stock setup might be turning twice that much at idle. Pump rpm is a big deal at idle, at 5000rpm not so much difference as the impeller isnt doing much there.

you are running a -12 off the left and right of your thermostat housing?

Yes. It's not yhe the factory housing but an aluminum piece.

I cleaned out my PM box, fyi