Enough CFM's to cool the closet?

OK so I was wondering if the htg 6" Inline Fan (Link to fan HERE) with 250cfm would be enough to cool a grow closet with either 2 x 150 watt HPS or 1x400 HPS and 1x150 HPS? +Rep for legitimate answer

No that is a "duct booster" fan, which have no ability to manage pressure. 2 of these 1 in, 1 out might work, but i would look into a real inline fan, a big investment, but worth the money. Also, if you (when you) get a carbon filter, the inline will work with it, the duct booster will not.
All cfm's are not equal, good fans will rate the cfms for different levels of water column, which is the pressure it must make to flow air.

I must say this answer did not have a father so it is an illegitimate answer.........

True about the above statement, but in terms of simple cooling- yes it will work. You'll have suitable temperatures, you just cannot use that fan to push or pull air through anything.

Hmmm alright well how about THIS? Would it need a duct silencer or would it be quiet enough without one? An can a DIY Carbon Filter fit over it?

The product description lists quiet and also "a perfect match for our 4" filter".. which means, if your DIY filter uses some sort of 4" adapter, and has decent throughput it should be fine.

btw- how big is the space being ventilated?