The difference between a 3700+ San Diego and an Opteron 148 is the name that's etched on the heatspreader. For all purposes we should concern oursevles with, they're exactly the same chip, just different names. Popular opinion is to get the Opteron because the chances of getting a highly overclockable chip are higher than those with the 3700+. Especially lately, there seems to be plenty of the new CACJE 0546 stepping going around, and they're exceptional overclockers (mine does 2.8GHz on 1.375v). The 4000+ San Diego really isn't work getting unless you have really crappy RAM, otherwise the x12 multiplier really doesn't do a whole lot for you.