I bought the fan years ago so I don't remember the cfm rating, I want to say something in the high 300's as its a generic 6"...The carbon filter came with the inline fan, it was bundle i got on ebay so I assume they were compatible. I remember the filter was a generic kind, nothing brand like Can, so I don't believe they had much specs on the filter. I had a fan speed controller and usually kept it at about 3/4's speed. There was not much ducting used, probably about 6-8 feet. The walls of the tent were always well curved in showing the suction, I think thats what was worrying me as I didn't want to suck out all of the carbon dioxide before plants had a chance to take it in. I think you're right about the tent holes not being completely sealed if I remember.
Has anyone ever doubled up on filters? I thought about keeping one big filter in the tent as normal, and outside the tent on the exhaust side of the inline fan, place a homemade carbon filter to extra filter the air. Does that sound pointless or do you suppose it could actually do some good?