Help needed: Abit IP35 Pro, Core2 Duo E6850 and reaching 4.0Ghz

I've had this board + chip for ~6months now, Running stable at ~3.7Ghz
Despite numerous attempts I cannot get it to reach 4Ghz.
Am I being a little too ambitious for Air Cooling? (AC Freezer 7 Pro)
I've upped the Vcore as high as 1.55v and the memory to 2.2v. I've loosened the memory timings to 6-6-6-18 and it stalls after POST. I've read all the guides by gilgamesh and Nelly and found them helpful, but I still can't hit the magical figure.
Does anyone have any suggestions?
It's getting personal:)

maybe your RAM just won't do DDR2 1000 ?

Yup, I'm slowly but surely facing up to that. Any recommendations for new memory?
Do you think it's possible to hit 4Ghz with this chip and board on air cooling tho, or is it time for me to dabble in the world of water cooling?
I was looking at a Swiftech kit (H20 Apex Ultra+) but it doesn't seem to be compatible with this board: it's a tight squeeze between the graphics card and the Southbridge.

imo you should be able to do 4.0GHz on that mobo assuming that all your other bits supporting it are capable of providing the environment.
I don't know if an AC Freezer 7 will do it though.

The sb doesn't get that hot.

How about a Tuniq Tower?
I bit the bullet and just bought 2Gig of Corsair Dominator 1066, hope it makes a difference.