My rig :
A7N8X Deluxe v1.06
Corsair 1GB LL DDR400 Matched pair

I had this comp. with a T-Bred 2600+ (333FSB) and Kingmax DDR333 RAM. The system wasnt stable even 1mhz above 166mhz FSB (turns out Kingmax parts I got are at their best possible clocks <grumble> ). I later got a 2500+ Barton with the above mentioned Corsair RAM. I plugged both in and got to OCing right away.

Turns out the Barton is locked. Anyhoo, I bumped the vCore 1.7v, vDimm 2.7v and FSB to 200. It wouldnt boot to Windows. After much experimentation, I found the sweetspot to be around 185-190Mhz. 195 is also stable (relatively, 16-18hrs b4 crash), but I backed off. I'm using the stock HSF with AS3, temps are around 53/57 (Socket/Diode) on full load. I'm getting a CNPS7000A-AlCu soon.

I really hadnt considered my T-Bred with the DDR400, but it seems I might get a new mobo and build a new system, or I might sell the 2500+ to one of my friends (hes getting a NF7-M, might have better luck) and get the 2600+ back in - IF it can OC good. Anyone have good info about how far it can be pushed? I dont have access to the CPU right now for stepping codes, but I can get them tomorrow.

Well sounds like the barton's multiplier needs to be dropped but if its locked then you can only bump the vcore no higher than 1.8 or you are SOL. Another thing it this mobo you have is PCB rev 1.xx and not the 2.00 then you are lucky to break over 185mhz on the clock. Just look at what I had to do with my barton 2500 to break the 200 barrier.

In this case if you cannot get a stable high clock on the barton then just go back to the tbreb 2600 and fiddle with the multiplier and clock with that one. However, Asus boards have issues with increasing multipliers so system clock is your best bet.

Barton 2500+ @ 2200mhz (10x220 vcore @ 1.8)
Asus A7N8X Dlx 440 FSB
1gb Geil GD pc3500 Dual Channel (2-3-3-6)
Segata 80gb SATA 8.5ms seek
ATI Radeon 9800 Pro(420/720)