San Diego's are exactly the same as Venices, except they have an extra 512kb L2 cache
Winchester's are the first 90nm Athlon 64's, which can't reach very high clock speeds compared to all the others.
Venices and San Diego's are the latest ones, which overclock really well, and run on low voltages (1.4v)
also like DiabloII said, they have SSE3 insrtuctions.
Intel first designed SSE3, it has 13 extra instructions, but Venices/San Diegos only use 11. the other 2 are for Hyperthreading