hi Tiny,

I run one of each......a one kw with 6 inch ducting and 440 infline fan.
Second one....cool tube....one kw....Adjusters from 6 in to 4 inch for your ducting and a 170 cfm inline (4 inch) and it works fine although you CAN tell a difference in that the six inch one you can touch the glass.......the four inch one runs hotter but still well within the range I need to get the light down.

Your 400w should be a breeze with those specs!!!