I think the problem is the fact that the 3400+ is a socket 754 CPU; they have a 1.6GHZ FSB and don't supoport dual channel, whereas the socket 939's have a 2GHZ FSB, and support dual channel. they also have the Winchester cores in 3000+, 3200+ and some 3500+'s
the winchesters have a 90nm core, use less voltage, run cooler and overclock much better than the Newcastles or Clawhammers
the Pentium 4's do seem to do better in multimedia apps that require more mathematical processing. this is mainly because they have more L2 cache.
if you're going Pentium 4, go for an LGA775
although personally I would say the socket 939 winchesters are the way to go at the moment