I had the GA-K8NF-9.
I ordered it when it was first released. When ordering it to this day, all websites show it with an active heatsink cooler on the northbridge.
Mine of course came with what you have on yours.
The motheboard was fine in the winter, but once it started warming up outside it started getting unstable and flaky. The heatsink got so hot, I could only touch it for a second.
Then about two weeks ago, it really started getting unstable. So I ordered a motherboard with active cooling on the chip, and all problems are gone.
I have always liked Gigabyte and their quality, but they really dropped the ball on this. The Nforce4 chipset simply gets too hot to be cooled with their crappy little heatsink (I have a 92mm intake and a 120mm exhaust fan, and have the Zalman 7700 AClu running at full speed).
I don't know what to recommend to you. They place the heatsink under where your video card will go, and there is hardly any clearance. The only thing that I did that helped a little was to add AS5 under the heatsink. The chipset looked almost burnt when I cleaned the thermal pad (what was left of it anyway) off of it.