Stock heatsink & fan:
Bus = 250
NB = x8
HT = 1600
CPU = x12
MEM = 500
Avg load temp = 58C
Max load temp = 62C
Prime95 = 5 hour
With the same setting as above and addition of Sanyo 109R1212M1021 (77.6 CFM, 32dB/A) donated from a PowerMac 8100/80AV PSU (custom duct as well):
Diodes on rotary switch used as controller.
Idle temp full speed = 25C
Idle temp min speed = 26C
Load temp full speed = 51C
Load temp min speed = 57C
Seems to generally stay roughly one degree below max seen when running Prime 95.
Mobo still crazy hot though.
The CPU should be able to go higher but I have stopped here because multiple components on the motherboard are too hot to touch for much time while under load.