Hi Tom, there is some more work that has to be done for STEP imports than for .3DM importing, especially for examining trim curves on closed surfaces.

Some CAD programs (and also STEP format) allow a trim curve to cross over the "seam" of a closed surface, which MoI does not allow and so such edges have to be found and split.

.3dm format does not allow that type of "seam crossing" trim boundaries so none of that needs to be done for .3dm import.

So in general there will likely be a performance improvement using .3dm format but it may not be very significant if the models are not very complex.

- Michael