Well 80 isn't so bad for lights on, I run in the 80s for majority of flower on purpose. I turn it down for the last few weeks(in my room where have control) but you can get by with that if need be. I'm honestly surprised you got it down to 80 in a a 3x3 with a 600. I run 315s in a couple 3x3 as well and they are in upper 70s majority of time(since I don't really have much control I honestly haven't had a thermometer in there for a over a year but when I did they were upper 70s). But I have a 6 inch fan cooling two 3x3 the fan is blowing thru the carbon filter which sets on the floor in between the tents (since only had one filter and fan for two tents) then on top of the fan is a y that has one 6 inch inlet and two 4 inch on the other side, from there I run 4 inch duct to the tents. It works great for me and I have plenty of negative air pressure( can tell from tents sucking in). It seems you can only cool a room so much with venting, how big is your fan and does it creative negative pressure on your tent that pull in the sides some what. If so your prob moving about all the air that you can from the tent. I have had success in the past using an intake fan to drop a few more degrees but it could have been situational since I had a window AC in the room the tent was in (really was before tents were common was a thing I built like a tent/room hybrid.)