SonDa5, as you were eluding to, I think, at this point, your TIM is the weakest link.
IC Diamond is an awesome TIM (I was part of the test bed for it at OCN before it's initial release and tested it on several rigs). However, it's only good, in my opinion, for CPUs' with non-modified IHS's.
I did a few test approximately 2 -3 years ago with some delidded 939's and a lapped AM3 CPU.
On all the tests I used a lapped Thermaltake big typhoon (lapped to 2000grit then polished out) and here's what I found:
The smoother and flatter the two surfaces are, the less TIM you need, i.e. lower viscosity (thinner). Thicker TIM's such as IC diamond, AS5, OCZ freeze, Tuniq TX-2, etc. are too thick and actually start working as an insulator rather than a conductor.
On both the delidded 939's and the lapped AM3, I found that if I just used the white "pigeon poop" TIM, it actually worked A LOT better than the high dollar TIM's. Reason being is due to it's low viscosity, the thin TIM will spread more evenly and there'll only be enough there to take up what small gaps there are between the two surfaces.
I was seriously thinking of just putting a thin coat of motor oil between the lapped AM3 and the BT just to see what the difference would be.
On a side note, the thinner TIM's also work A LOT better than the thick silver TIM's on GPUs as well. I swapped out the TIM on several "hot" ATI cards (4870's, 5870's, 6870's) and noticed the cooling was a good deal better than before.
Most notably, idle and load temps on the 4870's dropped 13C across the board. All that just from swapping out the TIM.