I think it is all in the drill. I have used the same nail eater 1" greenlee for a year with a POS Black & Decker drill. A couple of weeks ago I bought a Hole Hawg. Same bit totally different results. Wow this thing rocks! I have saved hours on every prewire. This drill has paid for itself twice in 2 weeks. I am sure my old bit is dull but it tears right thru. I am afraid a new bit would cut thru too fast hitting romex and pipes. I also do not go home in pain after a big prewire.
I watched sparky do an entire prewire with a Dewalt 18v. It took him over a week to prewire hi voltage in a 2500sq ft cabin. He had the advantage when working on the rickety scaffolding but I kicked his butt on the ground. I had to chuckle when I came back a week later to document my wiring and he was still at it. As I was leaving he asked about my new fangled drill.