Wow I tried almost this exact same thing last summer. Except I used 3 panaflos and a 10 in core. Don't waste your time, you'd need 10 or 12 80mm fans to reach the flow of a single 120mm panaflo. They basically just sit there and spin without blowing any air.
I ended up buying a pair of 120mm fans and throttleing them to ~ 6v with a controller. They barely spin but my temps are 5C lower and my video card can overclock an extra 25MHz.