When looking at fans, one thing to keep in mind is that more airflow is better than less - as long as you have the right size filter attached.

I've got a 3'x3' Hydrohut that I use. I had a lot of trouble with heat on the first grow I did in it, so I ended up buying a bigger fan to deal with it. I've currently got a 305cfm Canfan, with the 1900 Canfilter attached. That's almost twice the air movemnet I'm "supposed" to need, and the tent still gets warmer than I'd like.

One other thought, if you don't have one and can afford the cost, invest in a cool tube for your light. It'll make a huge difference. Wish I could afford one lol.