little confuse on ventilation. 5x CFM? or CFM /5? Yes i've been through the stickies!

So i've been doing a lot of research on ventilation lately getting ready to build my first cab and one thing ive been really confused about is the fan CFM requirements simply because people say 2 completely different things. A lot of stickies and common growing FAQs state that you want your air exchanged once every 3-5 minutes. Then to calculate in a little more headroom for ducts, filter, etc. Cool i get that. However a lot of people on the forums seem to be recommending fans rated for 5x the CF of their cabs AKA exchanging the air 5 times a mintue which seems a bit excessive. I'm going for a dead silent cab and i feel like exchanging air 5x a minute will create noticeable suction through the intake, also i hear plants in a vacuum is bad. So what's right? besides the sticky here i found another good reference but it's a little old, does this math seem legit? http://forum.grasscity.com/grow-room-design-setup/387277-answer-everyones-ventilation-questions.html

It kinda depends I guess.. is odor an issue? Since noise is I assume odor is as well and to keep odor from leakin outta ur grow space u need negative pressure or less air being blown in than is being sucked out-vaccum as u put it.. u want the air exhausted ATLEAST once every 5 minutes but more often is more preferable(imo) due to the need to suck thru a filter and ducting and manipulate the grow conditions . So the short answer is 3- 5x the size of ur room gives u better control of ur enviornment.

so basically people say to multiply you're cubic feet by 3 to 5 times so they don't have to do the math and still be sure you have negative pressure..? lol

That only factors in the fresh air needs of the environment, not the heat removal that may be required as well.