Opteron is AMD's top line, then the Athlons and then the Semprons
see specs:Opteron 144 Specs
' ">http://www.amdcompare.com/us%2...s.aspx?opn=OSA144BNBOXSempron 64 bit Specs
If that is a 939 pin Opteron 144... then I recommend that. I don't know what the UP stands for /tongue.gif' border='0' style='vertical-align:middle' alt='tongue.gif' />
The 754 pin motherboards are not very expandable at all and you will get more life out of a 939 pin solution.
The Opteron is the best chip that amd makes so it will be the most reliable and stable as well.
Overclocking Help and Links
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Great tools-> OC Bible v1.52 and Guidemania v1.2