I say if the neg pressure doesn't colapse the tent then run with it
Good job man, I think its hard to overkill most things in growrooms, except maybe nutes. Big fans, big filters, big lights, big AC's, big water and oxygenation, big plants:
=BIG BUDS!
... I was considering the 6" ellicent, but its only 309cfm and the can50 is 400cfm, so to be safe I am considering the Ellicent 200a with a duct-reducer....
Forgive me; I'm not sure I understand. If the fan is rated for 309CFM and the filter for 400CFM, where is the problem? Shoot me a PM if I can give you a hand.
Simon