RMClock will allow you to re-enable EIST and C1E, at least on the P5B Deluxe with the current BIOS. It should hopefully work with other boards to.
I'll have to try out this utility, even though I don't like when software controls my OCing. What version do we need to use for the C2Ds? (I think I remember seeing a regular and beta?)
I’m using version 2.1. You aren’t really using software for over-clocking; you are just using it to change the Speedstep settings.
It's hard to explain in one go, but the basic concept just like with laptop (except it's OC'ed this time) is to force down in multiplier and test voltage at every notch(multiplier) until you reach 6x. It's an extremely time consuming session as you're trying to find the lowest possible voltage for every multiplier at the set FSB.
As mentioned above, that's only possible IF RMClock provides more than 1.3525V
I suggest disabling all the intermediary multiplier values from within RMClock and just use the min and max ones available. It saves time and the intermediary ones aren’t often used that much anyway.
You can still go through this procedure regardless of RMClock not being able to over-volt; you are just limited to ~1.1x – 1.32x volts.
The way crow_smiling described with stock voltage would defeat the purpose of pure control overclocking. (Assuming RMClock does not support more than 1.3525V)
I don’t know what the term ‘pure control overclocking’ means, but the method that I outlined above is only useful and necessary in a limited number of scenarios.
E.g. if you enable C1E and EIST in the BIOS and overclock an E6300 to 3GHz using stock VCore, you will need a FSB of 429. This will mean at idle you will have 6 * 429 = 2.57GHz. The default VCore at idle with Speedstep is ~1.15V, which is very likely not enough for the CPU to be fully stable at 2.57GHz.
By using the method that I outlined above, the system will boot at 1.32xV and be stable and once RMClock is loaded it will re-enable EIST/C1E and set stable voltages.
This process shouldn’t be needed with an E6600 as the idle clock speed would only be 2GHz if the max speed was again set to 3GHz; 1.15V should be fine for that clock speed.
With an E6400 it is marginal. I tested an E6400 using this method, it was overclocked to 2.9GHz and at idle it was at 2.17GHz 1.15V and it wasn’t 100% stable. It’s the luck of the draw of course as other chips may do better.