One of the best if not the best single core AMD 939's is the AMD 3700+ San Diego. Good steppings allow you to hit or get close to hitting 3.0 GHz, some may go a little higher.<br />
I heard they are slowly phasing out socket 939's, i would imagine that includes single cores as well.<br />
<a href="http://www.newegg.com/Product/Product.asp?Item=N82E16819103539" target="_blank">Link to 3700+</a>
The X2'S Are being stopped in November this year. Production has stopped for all but the 4400+ and 4600+. <br />
The best single Core is the 3700+ San diego. <br />
The best for overclocking in the 939 series is the FX , Opteron.
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