Which option would you choose?

If you had the option of having limited air flow due to an air cooled 400 watt hood being only 4 inch diameter exhaust opening and I have a 6 inch 550 cfm fan, would it be better for me to reduce the venting thus lowering cfm and having it air cooled or just leaving the fan exhuast at the top of the tent and have all the air in the tent leave through that exit with a much higher cfm but not having the hood hooked up?

Also, it should be noted that if I didn't have to hook up venting to my hood then it would leave much better space for plants to grow.

would you have room for something like this?
http://www.homedepot.com/p/Speedi-Products-6-in-x-4-in-x-4-in-Wye-Branch-HVAC-Duct-Fitting-SM-WYE-644/202907305#.UaqdSZzNt8E
connect 1 part of the Y split to the hood with some 4in flex duct and maybe crimp down on the other 4in end so it pulls most of the air from the hood?
just an idea
GL

I always choose big tits...LOL

Get a 6 to 4 reducer