AirWolf
Honorary Master
D C is based on newer technology, but there are no dual core Celerons. The 4xx series (if you are talking about them) is based on the Conroe-L core but does not have 2 cores. The E2140 (based on the Conroe core) is dual core, running at 1.6Mhz, but is not a Celeron. The 4xx series running at 1.6 should be a bit faster than 3xx series running at 2.8, and will be a lot more overclockable.
Here is a good comparison
http://www.xbitlabs.com/articles/cpu/print/conroe-l-preview.html
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What's the best/safest way to overclock a cpu?