As far as specs go:
AMD Phenom II X4 925 (Stock Cooling)
AMD Radeon 4890
Case with 5 fans = lots of airflow
(All components are at stock values)
As far as what the motherboard alarm is set to, it is 60C, which corresponds to the 48C BIOS idle.
Not sure if this makes any difference, but I started up Prime95, and within a good 30 - 45 seconds, if that, the alarm went off.