Have just printed the first 300mm part. The mid top panel of the controller cover hit the supposed limit. However, the Ender 3 Max performed admirably. In fact looking at the gantry after completion, the printer could complete larger with ease.

To speak of the fit… Excellent. Once the parts were pinned together on the hard points the surfaces mated against each other perfectly. Only fault was that the assembly wasn’t easy. I think some time needs to be spend on the b-surfaces to ensure there is an slip on approach to assembly. at the mo there is a fair bit of bending and teasing needed to get the parts into position, needs to be much easier.