But we know it's possible and literally have a copy of the code that builds it. We just have to figure out how to emulate it. That puts a hard upper limit on how long all this can take. (It can't be "forever" since there is no requirement for the emulation to happen in real-time.)
As far as processing speedups, meanwhile, we don't even have 3D chips yet, just a single layer of silicon. Recent innovation: http://www.kurzweilai.net/first-true-3d-microchip-created-ca...
Given that a human brain is like 3 pounds of goo, and we have the genetic code that builds it, the rest is just biological reverse engineering + code refactoring of a binary blob without comments.
I am not saying this process is easy, but the idea that we can't make some solid predictions is fairly weak. We already do genetic engineering.
I wouldn't place much money on a true artificial mind still not existing in 40 years.