I'm no expert but,
He's got a pretty strong O/C already, on a Epox 8RDA+. Yet.......
1) standard heat sink on NB
2) the NB heat sink is cool to the touch after 6 hours running
3) I'd expect to get toasted fingers on that NB after 6 hours running if it were making good strong contact.
Suggests to me that he's got poor contact between that "standard" heatsink and the NB. On that MB that's about normal.
I'd suggest a copper Iceburg active chipset cooler on the NB and some AS3 or Nanotherm silver XTP. I think your northbridge cooling could be the problem.
Won't cost much to find out.
edit:
If you're brave you could also lap that NB flatter, @ your risk of course.