Which Chip should I use??

[cdsonic]

Which AMD chip would be better to upgrade to the XP2500 with the Barton core or the XP2600 with the Thoroughbred core?

 

[PliotronX]

If left at stock, probably the 2600+ because of its frequency advantage (2.06GHz vs. 1.83GHz). For overclocking, get you a 1700+ TBredB, should take you up over 2.1GHz for half the cost