You should remove the option of a 2x3 foot board completely while it's out of stock, instead of disabling it and writing "Out of Stock". Better yet, A/B test it

You should remove the option of a 2x3 foot board completely while it's out of stock, instead of disabling it and writing "Out of Stock". Better yet, A/B test it. My bet is that people are seeing the option they want, saying they'll wait until it's in stock, and then promptly forgetting you ever existed. If there's no better option to wait for, more people will buy one of the other options.