40x sounds pretty conservative to me. I did graduate school in math (did not get a Ph.D.) and my advisor indicated that he assigns problems assuming a 200x multiplier between his capability and the students'. That is, he'd assume that something he could see how to do and could execute inside of a week would be a good thesis problem to keep a Ph.D. student busy for two years.

As far as the 10x programmer stuff... Obviously there are 10x and probably even 100x programmers. They're the experts, and there are not many of them.