Well, I think I've changed my mind... Again...

I have decided to up the cabinet dimensions to 28"x37"x65" tall. I'll use a 400 watt HID (switchable bulb), a 6" elicent inline fan and 6" ducting. I'll still be making my own carbon scrubber (6" inside, 8" outside, about 12-15" long) but will likely just buy a cool tube so that it fits into the 6" ducting without reducers.

The system will be:
DIY scrubber ----->6" cool tube---> 6" elicent inline----> possible DIY duct muffler-----> out of cabinet.

Total volume is about 40 cubic feet. I need at least 40x3=120 cfm to clear the air 3 times per minute. I think the 247 cfm elicent will be fine even with the resistance due to the scrubber and cool tube. What'ya think?

I have noticed that elicent makes two 6" fans, the 150A and the 150B. One is 247 CFM, one is 309 CFM... Now I just have to pick one... Any recommendations?