Is this Negative Pressure Overkill??

Hey, guys I have a tent thats 36"L x 20"W x 63"H im going to be putting two 5 gallon pots in there. Plants will be vegged in another box LST then moved to this tent for flowering LST/Scrog. Im going to be using a Cool Tube 250w HPS vented out the top of the tent through a hole I cut into my ceiling that leads to the attic which only has to go 3 feet to be vented outside. So from tent the max venting from grow tent to ceiling is roughly 6 feet then roughly 3 feet to be pulled out the side of the attic. I understand that in order to have negative pressure I need a 4/1 ratio of exhaust to intake. So my question is would this work or be over kill? My 250w HPS vented to a 434 cfm fan pulling to a carbon filter then a couple more feet to outside. With a 100 cfm fan on the bottom of the tent for intake.

Also side question since I am pulling straight up should my fan be inside the tent or outside the tent?​