Amd usually give a sizable performance increase each new gen. They probably won't be able to match Nvidia for power consumption but as long as they don't take a leaf out of their competitors book and do what they have been doing most gen's it should be a good increase. If you don't know real spec's you have to judge by what they do normally. Can't see them launching the 390 at the same performance as the 290 or only a bit more as that would be suicide.
Ahhh so you are guessing then. Also, the only thing about a launch is a site claiming Q1 of 2015 for a launch and that could mean March of 2015, so 3 months wait becomes a 6 month wait and using my own impatience, I struggle to wait a week when something is out already that has what I need.