400 cfm inline or 720 cfm for 800 watt setup

Which should I use a 720cfm inline fan for a dual 400w cool tube or will a 400cfm cover them perfectly fine?

I can't say for sure, I only own a 400cfm fan. I don't know if it's enough for 2 seperate cool tubes, but it moves a fuckload of air I know that. on the other hand, if you get the 720 and it's too much you can always get a fan speed controller and dim it down to a reasonable level....