I was not suggesting anyone buy the socket 754 CPU, only pointing out that there were other cores than the Skt 939 San Diego with the 3700+ designation.
Opterons are server quality chips (some are dual core) that give you the most bang for the buck and are great overclockers. They are a more cost effective way to get a dual core CPU than the X2 series. They should not be confused with Semprons which are castrated Athlon 64s.
As long as you stick with socket 939, the A64s, X2s and opterons will all work in the same motherboard. (some might need a BIOS upgrade).