How much CFM do I need for a 4x4x6.5

I was thinking of going with ac infinity cloud line T4 4 inch. I will also be adding a carbon filter and ducting but I doubt any bends will be included

A 6" fan is better suited for a 4x4 tent

Around 400cfm is ideal that’ll give you around 4 exchanges/minute. Duct your exhaust out of the room your tents in if possible otherwise you’re just recirculating

I have a T4, go with a T6 or even T8. Low speed to keep it quite and higher flow if you ever need it.

Yeah I agree with the T8 or T6. I don't have the T6 but the T8 has been a bad mamajamma for me. In a 4x4 I can keep it on 2-3 (depending on the season) and you don't know it's even running. I'll warn you though if you crank it up to much it will probably suck your tent inside out and then spit it out the other end lol. Seriously though it's got some power. I think you could easily run two 4x4s with it if needed