No matter what I do, my eVGA 680i A1 board seems unable to go above 400Mhz with my Q6600.
To get 3.6Ghz (400x9) stable, I had to set the voltage to 1.55v, and going even to 1.7v doesn't allow me to get anythig higher than 3.6Ghz stable.
That means it's my North Bridge that is the culprit, but I have it cooled by an HR-05 with a 120mm S-FLEX fan, and it's the A1 version.

So, what do I do? The temps never go above 50C with my modded, ducted and lapped Ultra 120 eXteme with a dual-fan set up.

Thank You

That's perfectly normal for 680i chipset motherboard, which is pretty much the worst for oc, other than 650i. Read around the forum, the highest stable oc most people with 680i on q6600 is 2.8ghz. Don't push chipset voltage too hard or it'll die on you. 680i runs hot even at stock.

Nvidia 680i boards have had a lot of troubles. The 780i boards are supposed to be better, but not by much. This is where a X38 or X48 board is a lot better, though if you're using SLI, then they are useless. In the case of using SLI, I'd look to a 780i board from ASUS or DFI, perhaps even Gigabyte for best results. I'm using an ASUS X48 board because I choose Crossfire. The X38/X48 boards seem to support a FSB up to the area of 450 -475, depending on the individual board.

It took me a bit to get my 680i LT (A2) to any stable OC (first stable spot was 3.3Ghz). I've been hearing on this and other forums that there are FSB "holes" on the 680i boards where they simply won't run stable. Generally I'm hearing the same sentiment everywhere, "680i boards suck for OC'ing Quads".

I can't do 3.6Ghz cause I don't have enough cooling capacity. At 3.32Ghz I'm running up to 66c (high core temp) with Prime 95 running me at 100%.

You might try altering the FSB to something other than exactly 400x9. I've heard changing a couple points in either direction can sometimes cure the problem on these boards.

Don't do it. You'll kill the board.

LOL I'm certainly not going to try for 400x9 on my own board. The board is only rated for up to 333x9 anyways. I guess my whole point is, changing the exact FSB value a couple points might help, as I've heard the 680i's have invisible FSB holes. At certain values they just won't run.

I'm hearing that OC'ing the 680i's with a quad is difficult anyhow, let alone reaching 3.6Ghz....

I can't afford to replace my system, so I'm fine with my 3.32Ghz.

You should really keep an eye on the chipset temperature, especially if you can't afford to replace the board. If it's too high, you might want to tune it down.