Isnt it much easier to sing above your speaking range? I find that when I use support from the diaphragm when singing with power I feel like I am drawn higher. Some teachers, including mine, says that for higher notes it is important to think "down". I like this a lot. I really feel like support forces me up. When I hum a note with support i often end up on F#3 which is really my highest speaking pitch (if just talking normally). I use classical singing rather than pop singing. My power is above the speaking range. I feel like there is a mechanism in singing that forces my up to the higher notes.