Now that there is so much stir around the upcoming Conroe processors launch, some overclockers may have forgotten that there have recently appeared 0.065micron Celeron D models that are still based on CedarMill C1 core stepping. In the meanwhile this core stepping is quite rare among retail Pentium D 9xx CPUs, however Celeron D 356 (3.33GHz) and Celeron D 352 (3.2GHz) have it by default. Moreover, these CPUs should become cheaper in the end of July and by fall they may even acquire new D0 core stepping.
By the way, a lot of mainboard makers mention in their compatibility list that there might be 0.065micron Celeron D processors with B1 core stepping. Of course, this is no catastrophe, but these processors may overclock slightly worse. From the economical standpoint it is more beneficial for Intel to use old core steppings for budget CPUs.
We know of a few cases when Celeron D processors on 0.065micron CedarMill core overclocked to 5.0GHz with powerful air coolers. It was not only the significant frequency potential of the 0.065micron core, but also the high nominal clock frequency multiplier of the CPUs. XtremeSystems.org forum reports the results of Celeron D 356 (3.33GHz) C1 core stepping overclocking. The CPU reached 5.4GHz frequency with only an air cooler.
To be more exact, they only managed to take a screenshot at 5.4GHz frequency, however the Vcore was relatively low: 1.4V. And at 5.1GHz frequency and nominal Vcore the CPU passed all the tests flawlessly. The 50%-60% frequency increase without much effort ?far not every CPU can boast something like that.
By the way, it was a regular boxed processor that they got from a regular computer store. Here is what the high nominal clock multiplier of 25x can do: to reach 5.4GHz frequency they hade to raise the system bus frequency only up to 218MHz. Celeron D processors formally support 533MHz bus, which corresponding to 133MHz system bus frequency. Celeron D 3xx models based on 0.065micron core have twice as large L2 cache than the predecessors: 512KB against 256KB. Larger cache also affects the performance level, and of course so does the excellent overclocking potential.