ventilation help

OK, so first of all can someone clear this up for me. I've heard a lot of different opinions on how much air displacement you need for your room. Some people have told me to be able to evacuate the air 5 times in one minute(which seems over kill to me) and others say that once every 5 minutes is fine.

Second. I have a room that's 3x8x8 so 192 cubic feet. I was looking at fans in between the 300-500CFM range, or does that sound like too much and should I look for a 200-300CFM fan.
 
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