When overclocking, I find that isolating the components works best for me. This way I know what the limiting component is. In your case, this is easily achieved.
From what you have, it seems any overclocking beyond 333FSB is going to push your ram beyond 800mhz at CL4 timings since right now at 333FSB the ram is set to work at DDR2 800.
Step 1: Finding motherboard FSB speed
1. FSB: Memory Mode => Set to Unlinked (so that FSB can be overclocked independently of memory)
2. Make sure you relax all the timings on the ram (5-5-5) and set any performance options in the BIOS to defaults (such as any Turbo/Enhance levels set to their lowest to not strain the motherboard).
3. Lower the Multiplier Factor from 8x to 6x.
4. Fix PCIe frequency at 100.
5. Raise the CPU operating speed from 333 to 375 then to 400, then to 425 and each time at boot run SuperPi 8M and see if the system is stable (at this point you could try running Prime 95 small Ftts to stress the cpu/mobo) If the system passes all the way to 425, then you know your motherboard can easily do 425FSB without any adjustments.
Note: Even at 425FSB x 6 multiplier, your cpu is still running at 2550mhz; well below its 2.66ghz nominal frequency. It is important to always remember this since at some point FSB speed can become so large that you'll have to increase your cpu voltage even at multiplier of 6x. Keep this in mind since you don't want to blame the motherboard on not attaining high enough FSB when you forgot to increase cpu voltages
However, you might have to adjust CPU VTT Voltage by +0.1/+0.2 and NB voltage by +0.1/+0.2 as you start exceeding 400FSB. So do this until you reach your desired FSB speed (In this case I would check if your mobo can do 460FSB because if you were to move the multiplier back to 8 you'd have a top speed of 3.68ghz which is probably more than enough for your processor, given the cooling you have).
Step 2: Finding your CPU speed
Keep everything the same (ie. whatever you needed in terms of motherboard voltages to reach 460FSB), except:
1. Lower the CPU operating speed back to 333.
2. Increase the multiplier to 8x
3. Now you are going to increase the cpu operating speed from 333 to 375 and run SuperPi again on that boot. Keep increasing the FSB until the system either crashes at boot or freezes or doesn't boot. That means to go beyond this speed you need to increase your CPU voltage. ==> so slowly increase it from 1.35 to 1.375, then try booting at that speed again and so on. At some point you might be at 425FSB and voltage of say 1.400 and the system just doesn't boot anymore (check temperatures with CoreTemp 0.96 and run Prime 95/Orthos to stress the 2 cores).
What usually happens is that at some point a lot of additional voltage is required to increase cpu speed just extra 100-200 mhz. Then you'll have to decide if the temperatures are acceptable or how much you want those 200mhz. For instance if you need to increase voltage from 1.40-1.425 to 1.500 just to get to 3.6ghz, then I wouldn't consider that worthwhile.
Step 3: Finding acceptable motherboard/cpu voltages
Now you know that your mobo works at (say 460) and your cpu goes to say 425. But remember how you set voltages on the mobo to go to 460 but at 425 you needed much less voltage (for example). In this case you lower the NB and CPU VTT voltages to levels enough to sustain 425 FSB (or whatever FSB you end up with).
You can also play around with cpu voltages as well in a similar fashion to find lowest acceptable voltage.
At this point you run Prime 95 for say 12-24 Hours (small ftts) and see that the system is stable. If it isn't, then you might have to increase cpu voltage a bit more, or lower the FSB speed.
Note: make sure to run CPU-Z to check your cpu voltage since what you set in the BIOS and actual CPU voltages won't necessarily match (a lot of times it's lower in reality due to vdroop)
Step 4: Finding memory voltages/timings
Now that cpu and mobo have been finalized, you can figure out how you want to run your ram.
So set it to linked 1:1 ratio and still keep the timings at 5-5-5. So for example if your FSB is 425 you'd be running DDR2 850. If the system boots at just 1.85V, then you'll start lowering the timings on the ram until you are required to increase the voltage (if it becomes unstable) You might find that even at DDR2 850 you need to increase memory voltage already even at CL5 = so do that. It's safe to increase cpu voltage to 2.1V (but 2.0V should be more than enough for DDR900 even.
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Hope this helps.
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