I have the A7N8X DX, and the NB heatsink might just be stuck. I got mine off and replaced it with a Crystal Orb....and didn't see any increases. You're right smokin'...the stock NB works well.
I didn't lap the NB chip, even though it isn't flat as that'd probably void my warranty. I like to be able to set things back to stock configurations....besides it'd be a lot of labor and tough to do to a chip while it's ON the mobo. Heatsinks are easy in comparison.
Mpetrie, I'd wager you can remove that Zalman, but it'd take removing the mobo and pinching the posts on the backside to release them. If it works I'd leave it. :2cents: