Thanks for the advice everybody. Full Field mode worked *great* last night! It was bang on and worked the first time. Linear worked just the way that I would expect it to. I even tried polynomial mode and it picked the same focus point as Linear, though it didn't seem like it took enough data points to come to that conclusion. I'll have to play around with it more before I put my trust in it.
Woot! I'm really happy with how things are working. I'll still probably switch to the 5:1 stepper at some point, but I'm not in a hurry.