I did that with my old 7950 gt. I forgot who posted it when I made it though... so belated thanks revs!! It droped core temp 15c. It was a single slot cooler also.
My current method is much simpler. I took off the 230 mm fan on the side panal and replaced it with 4 78 cfm red led fans. it sounds like a jet now but I game with a headset so I dont care. PIC
right now I have 300 cfm + - of air flow in my case and I hope to bump that up to 350-400 soon. the fan change made a 5c drop in cpu temps, I'm not sure about the northbridge exept that the temp alarm which used to go off every 10-15 minuites has not gone off once even if my room is at 80f.