If you want to see some decent battery life benchmarks for various phones I recommend checking out anandtech. They do about the best job I've seen of giving you a real world picture of what battery life will be like on most high end smartphones. At least their results on the Droid X mirror what my results were with that phone (I've now got an optimus S... which has really good battery life btw).
As for the Evo 3D... I'm really curious to see how it does on battery life. I've been pleasantly surprised with the battery life of other dual core phones so hopefully Qualcomm can be competitive in this area.
One thing that I'm sure will be significantly better is 4G battery life... the 4G radio in the Evo 4G was first gen, the 3D should outdo it handily.