I had a Zalman heatsink and fan replacement for one of my past video cards. The noise difference was incredible. The only downside was that the combo was so monstrous, I had to remove my video card every time I took my pc home from college and carry it separately. It probably would have cracked the motherboard otherwise

There was a definite improvement, though. I highly recommend their products. I've been using a copper Zalman HSF on my CPU for a couple years now, and it's worked like a charm and is probably the quietest fan in my case.