brokenAvocado:
Ok, but I wanted to change to a servo because the small dc motors don't have a wheel to fit on, and that's really the main reason why I wanted to change.
I have no experience with the micro servos, but keep what Duane said about speed control in mind. My Dagu standard CR servos aren't the best for speed control either, but I only run them at two speeds anyway - stopped or flat-out. 
Also it would pay to ensure that the Adafruit micro servo wheels will fit the servos you decide to buy. If micro servos are anything like standard ones, the shafts will vary from manufacturer to manufacturer, with different numbers of splines. That's why I bought servos that were supplied with wheels.