Thats a good question on te computer fans,im not a big fan of using comp fans though,their build quality is questionable for our purposes & in no cases are they meant to be ran in conjunction with any type filter or anything that would restrict air flow.
Another thing ive noticed about computer fans,this came to me when i was messing with a regular window fan in my bedroom,my wqife bought me a new fan for the room,i put it in the window & couldnt feel shit & it was on high too,i got to looking at the slim line design & the twist to the fan blades was minimul in order to keep the slim profile,this resulted in very little air being moved more than a few feet past the fan,my old fan had a very deep twist to the blade & could be felt from all the way across our bedroom which is 14ft.
Every computer fan ive ever used had that same very slight twist to the blade,im not sure they are fit to move air in a grow op unless its a very small enclosed cabinet,not because of lack of cfm but lack of their ability to throw air long distance,something they were nerver designed to do from the start.
FYI you can buy 4inch,6 inch & 8 inch inline duct fans at home depot for $20 for the 4 inch models,$30 for the 6 inch & $40 for the 8 inch models,i know for a fact that these type fans move asir long distance because i use them & the filters will work with the inline fans.