need an expert on cooling + rep

not to bad if your hood is sealed. I have the same summer time problem. on really hot days you may have a problem, but any air flowing at a high volume helps as long as the temps are lower than the bulb.

as far as pulling 200 cfm into your cooled area not a problem. You probably let 100 cf in every time you walk in the door (probably more.)

Is there any way to test cfm output other than what a fan is rated for?
I would love to know how many I am pulling right now.

Also I can give a second speed controller a try like suggested, but will a centrifugal fan only go so low?

With the controller I have now it doesn't seem to slow it down any more once I get to a certain spot on the dial.

use the fan you have

if you have a fan like in that picture that bitch will pull a golfball through a garden hose

set up a vacuum closet or a branch like the one you have with three lines not 2 (try not to make the airflows cross but rather merge into one anther like an on ramp on the interstate

with all lines being equal technically all cfms should be equal. ( around 150 - 200 cfm per line you ma have to slow the fan down on cooler days.