Well, looking at the pictures of the dancers on the speeder, it looks as though the speeder is longer than the full body length of two of them. Your MPC scale makes it ~12 feet, but it does look longer than that.
I would expect the older (1980) MPC kit to be less accurate (because we weren’t as obsessed back then!) and Bandai seems to really sweat the details and accuracy.
I wonder if dimensions given to the model companies are so different because the numbers they were given were simply derived from different measurement points?
In 1980, licensing of movie tie-in products was still in its infancy. I wonder if people approving a model kit had access to the information they needed or if they just “punted”?
The Bandai kit, only what, 5 years old? Is built with all of this scrutiny, the licensing people know that it matters to the fans and they need to get it right. I could see them even knowingly changing it to make it fit better in reality - 5.7m (~18 feet) does make more sense.
Maybe the Bandai length includes the bit of harpoon hanging out of the back?
