With an 8" exhaust, you need to have 4 6" holes to have just over twice the intake area of your exhaust. If you have the 8" going for exhaust, I would have all the 6" vents open and any of the rectangle windows in the tent open. Especially since it's in a room that only holds the tent. Just need to make sure the room is light tight.
Pull air from outside the room(coolest air possible, basement air works nice) into the room and thru the tent, out of the house. That should help lower temps some. The way you have it now. If your running air from outside thru the light and out of the room, you could air condition the room and that would prolly help keep temps lower. Only thing with that comes the need for exchanging the air in the room, or having co2 supplementation.
Pull air from outside the room(coolest air possible, basement air works nice) into the room and thru the tent, out of the house. That should help lower temps some. The way you have it now. If your running air from outside thru the light and out of the room, you could air condition the room and that would prolly help keep temps lower. Only thing with that comes the need for exchanging the air in the room, or having co2 supplementation.