Funny story about NB cooling. When I ran it previously, I used a Tek Slim sitting on the stock heatsink. I had no issues pouring the Tek full pot and the probe dropped down to about -190 or so. This is when I hit 670 FSB for the first time.
On my most recent run, I actually acquired a legit NB pot and used heatsinks on the VRM's, etc. I found out that the cold bug on the NB is about -45°C. Basically, putting the Tek on the NB heatsink was virtually ineffective since -190°C on it didn't even translate to -45°C at the chip.
Next time I take the board cold I'll see if the NB pot makes a difference for FSB since I was just pushing my E8600 last time and FSB didn't need to be above 650 or so with that for the benches I was running.