Have you thought about using a hall effect sensor instead of the optical one? It's also possible to tap into the motor's own sensors. You'd get three samples per revolution.
I did this as a test early on but I want to test brushed motors as well so I changed the design. I thought it would be easier for my to manufacture an optical wheel. That was before I realized that PLA doesn't work. I also have concerns that a hall probe may have speed related, variable delay problems