That looks good. From my perspective, I don't think it will impact the coolants temps, though I guess I might help a bit. My desire is to drop the overall underhood temp, because during the summer mine feels like an oven set to broil.

 

Came across this video, while reading this thread.

 

Things to consider: The area in front of the windshield has high air pressure because the air builds up in front of the glass. A vent where you are proposing with reduce the air pressure differential at the radiator. Remember, good air flow through the radiator requires the air pressure on the backside to be less than the air pressure on the front (grill) side. A hole in the hood will raise the air pressure under the hood therefore decreasing the pressure differential and thus decreasing the airflow over the radiator. Everyone has seen "cowl induction" setups. That type of vent feeds the intake. The engineers are taking advantage of the air pressure in the cowl area for force feed the intake. If you want to increase your radiator air flow you do that by venting the under the hood area to a low pressure area. That is the idea behind the hood vents on the sides of the car behind the front wheels. What you are proposing works great at rock crawling speeds by allowing the heat to escape but kills your fwy speed cooling.