Small Grow Tent Ventilation

Hi All -- I have a 2x4 Gorilla grow tent on the way; it's just about 7 feet tall, making it 56 cubic feet. I need to ventilate it through a carbon filter, and my first thought was a 4" inline fan, but it seems that these are all rated at something near to 190 CFM. Even allowing for a reduction due to the filter, that's 2 or 3 complete air changes per minute. This seems like way too much, especially as I will be lighting it with LED lamps, so there won't be a heat problem (and in fact, at least for the winter, I'd prefer to lose less heat if possible -- the room it's in is about 65 degrees all winter, so any heat from the lights will help).

So here are the possibilities as I see them:

1) Get a 4" inline fan (with a carbon filter) anyway, get a speed controller for it, and turn it down to low. Maybe that's the ticket; it does bother me, though, to no longer know what I'm getting in terms of CFM.

2) Same idea as (1) except with a 6" fan, only because I've heard some say that the 6" fans tend to be higher quality and quieter. (Seems a bit crazy, though, to be going bigger for a small tent...)

3) Some sort of DIY solution. In particular, here is an interesting thread in which someone describes a homemade carbon filter connected to a (very quiet) Panasonic bathroom exhaust fan: https://www.icmag.com/ic/showthread.php?t=45196

Thanks in advance for any suggestions.

After obsessing about this for the past few days, I just ordered a Soler and Palau (S&P) TD-100 4 inch inline fan, rated at 101 CFM. Shopping next for a speed controller, then a carbon filter...