Mining by hand?
For me, mining is about values/time, not (values/volume)/overhead. So try to beat 3 Combustion-Engine powered Quarries by hand and you will loose. Mostly because you have to deliver the stuff somehow somewhere and that takes time.
But actually for me there are 4 techlevels of mining:
1. Mining by hand. (usually strip-mining for Diamonds
2. Mining by hand with Turtle support. Usually my Turtles dig long tunnels from the main shaft, come back, move three blocks to the side an wait for me to empty them and start the process again. They also put down torches so I can easily inspect the tunnels.
3. Quarry Mining. Usually in combination with an fully automated ore-processing factory. Fuel comes from a Bio-Fuel factory. Actually this is the stage I'm usually staying.
4. RedPower Frame Mining. On my server I once had a guy who used a full automatic solar driven RP2-frame with BC Mining Wells. He just cut the world in half and made so many ressources he was selling his dirt to other players who only specialized in recycling that stuff. It was a giant monster machine and im not shure If I will ever build such a thing by myself since it makes the world a lot uglier.