I use a 435 CFM Hurricane 6" for my 4.5'x4.5' tent, and I keep it on low, with loads of negative pressure sucking in the sides of my tent. I wouldn't even want to know what 950 would do... like lowryder said, your tent would "implode" hahah
I use a 430 cfm in my 5x5 flower tent.
It runs at full power 24/7 with 2 - 1000 watt lights.
At night the tent gets closed up and the negitive suction works great, I leave the 2 bottom tent vents open and pull from above, fresh air all night, less chances of high humidity and mold.
The tent is 5x5 with 2 - 1000 watt lights, the average temp during the day in the tent is 78-82 and the room temps outside the tent are 66-73.
The temps inside the tent get lower at night with the lights off, sometimes in the 60's.
If it's colder at night I'll turn down the fan via the $15 controller attached to it.