Guys, the NB really runs hot. If you have poor case cooling, NB temps gets up to 80C. I've tested on an open bench (28C room temp) with/without a 120mm case fan facing towards the mobo and here are my results based on the stock volt, stock NB heatsink&TIM:
With Case Fan:
Idle: 54ºC | Load: 57ºC
No Case Fan
Idle: 82ºC | Load: 84ºC
For an 80nm chip and at only 1.28V, I think RD600 outputs quite a lot of heat. The stock heatsink gets way too hot without case cooling and it stays hot for about 5-10 minutes even after shutdown. I had to wait a few minutes to remove the NB heatsink as it was too hot to touch. My max bootable with the stock NB heatsink was around 490FSB.
Currently testing with a Thermalright HR-05 and NB temps dropped by about 10ºC. I'm getting around 50ºC (w/case fan) and 74ºC (w/o case fan). I strongly suggest swapping out the NB heatsink as soon as you get the board. Will try out higher FSB with HR-05 installed