I currently have a G0 Q6600 and am just using the stock heatsink/fan now. It's running comfortably at 2.6, but I'm sure I can easily go higher with a better cooling setup. The problem is my limited space. The Intel heatsink is about 3/4" away from the PSU, which would give me a few options, however I only have about 1/4", maybe a millimeter or two more, of clearance from the heatsink on the northbridge. The motherboard is an ASUS P5N-E SLI(which I'm completely happy with other than this problem) So any recommendations on what I could use? I'd like to get 3.0 out of it if possible.
Small cases run hotter anyhow. You can go up to about 2.8 without any heat issues on the stock heatsink provided you have good airflow with your fans and a case that tends to run cool (usually because if it's size though some small cases are designed quite well).
That aside, there are lots of choices for aftermarket coolers, what you need to look for are ones that are supported by the manufacturer to be able to cool a C2Q and don't buy an offbrand and you'll be fine.
You read my mind. I was thinking of suggesting the Antec 300 and the Xigmatek S1283 with the backplate. I didn't post the links because I have grown weary. Too many links to the S1283 and backplate, you would think I'm a shill. Check my old posts or ask.
The mobo will take it easily. Making concessions, due to the case, will definitely result in considerably higher temps.
I looked at your board and see what you mean by the restrictions with the NorthBridge heatsink so close to the CPU socket.
I have a very similar situation with my DFI board.
The HSF cooling solution I used was the Arctic Cooling Freezer 7 Pro. I will fit your needs very nicely.
If you wish to go the Xigmatek route and spend that extra cash I would recommend that you get the better Xignatek cooler.
XIGMATEK HDT-S1284EE with the bracket.
The Thermal Resistance is only a few hundredths better that the Freezer 7 Pro, making it a great value.