Well, first off, in most instances, the case being open hurts temperature and airflow. The case is designed to conduct airflow, and by leaving it open, the fans are blowing some of that air into the open. Second, what are you using as a conductor between the HSF and CPU? Right now I've got a 1ghz ahlon with a stock Foxconn and the temp stays at around 105F with a heavy load. I'm using artic sliver I. I'll let you know what happens when I finish my current PC. Between the Lian-Li PC-12, an alpha HSF, and the artic silver, I would expect my next system to be very cool. I have a delta fan and a sanyo denki fan, and if the temp difference is not too much, I'll stay witht he sanyo because it is so quiet.