Are you using Rhino in wireframe mode?

If so then that would make a difference - MoI does not have a wireframe mode. Instead MoI displays objects with a shaded view. Displaying a shaded view is a much more realistic view, but it does require more memory for the display meshes, and some additional time to calculate them.

In the future I want to add a wireframe mode to MoI, it would be useful for situations like this with dense and complex files.

- Michael