Beware, 40mm fans can be very very loud because of low surface area. All depends on your tolerance for noise.
My Asus M2N-SLI deluxe (AMD, but bear with me) has that passive heatpipe cooling on the chipset, and I get about the same temperatures Assman gets. Not sure how much warmer or cooler the nForce 5xx chipsets are compared to the Intel ones, but it's plenty cool for me...and silent