What I called medium roast (what I liked for drip) I was stopping just at the onset of the second crack. I liked that result. When I went beyond that, the flavor seemed to go down and it just seemed burnt. But for espresso, I prefer a darker roast and never figured out how to do it without destoying the beans. I don't know how people do the darker roast (like Starbuck's espresso, Italian, and French roast) without ruining the beans. I like Starbucks, so that's what I use now for espresso drinks. I never tried any other method besides the popcorn popper. When I first tried, the popper I had roasted REALLY fast, so I put the dimmer on it to tone it down.
edit. Just read your roasting write up. I have probably been roasting too fast. Never looked into the proper time, or played with slowing it down more. I adjusted to a point where what I roasted tasted as good as the roasted beans from the coffee shop that I bought my green beans from. But like I said, when I tried to make espresso from anything I did, I didn't like it as well as Starbucks, so I quit roasting.