That's a shed load of air exchange for a single 600 watter
Fanleaf...
Are you taking your readings from in the light area? If so, you get a false reading, can't remember what the term is, and it doesn't matter anyway, it's just false.
Make a little hood or summat from cardboad so your thermometer isn't in the light.
Also remember, it doesn't matter how powerful your fans are, the coolest your gonna get the room without aircon is the same temperature as your intake. I know that sounds kinda obvious but some people seem to think that fans magically make the air cooler than it was before you brought it into the room.
If you can do mate, measure the air temp at your intake (before it gets sucked into your 4" ) then measure it as it leaves your exhaust.
I've got 5 of those tents mate and your extraction is way, way, way enough.