I put a 445 cfm on a clone tent and it sucked the sides in quite a bit..

I'd go with 2 fans.. one for your light with it's own intake and exhaust, running when the light is on. A second fan to vent the tent with a temp controller. This would let you use a smaller fan for the tent itself. A 245 cfm can fan would do that nicely completely cycling the air in the tent just less than once per minute.

Last.. don't think heat isn't an issue, with a 1000 watt HID light in a tent you can cook some plants.

Peace, Farmer Rich