The 3400 is socket 753 in this example which is an old socket and slower, and lacks dual channel ram.
However, if you find a SOCKET 939 3400+, it exactly the same as another newcastle SOCKET 939 3500+. This is my own deduction after hours of reasearch, feel free to test it.
Can someone tell me what the hell an Athlon 64 3300+ is, I've seen in advertised by Best Buy dozens of times now and I wasn't even aware such a thing existed.
They're pretty much right, the Newcastle/Winchester Architechture found in the 3500+ in superior to the Clawhammer achitechture of the 3400+. I don't even know the details very well, but I'm sure someone trying to explain it wouldn't really help the situation either.