[tgm1024]

Changing the speed higher will usually air lock the blades where they do nothing.

I don't think I understand this. What is "air lock the blades", and why "usually"? Do you mean pushing the speed faster than the atmospheric pressure will allow feeding behind it? (It always comes down to this sooner or later).

But I've modified many DC fans under different scenarios, and even over-drove an AC (<---note!) fan by pushing a signal generator through a 1000W amplifier as an experiment. (I was young and immortal at the time.)

In every case, a faster spinning fan would throw more air and draw more into it to sustain the reaction.