Hi 2kemon, well MoI is not polygon based, so there isn't really any concept of a poly limit in it. Objects in MoI are made up of NURBS surfaces instead of polygons (although polygons are used for the display since that's what video cards know how to render).

There is not any predefined limit on how many NURBS surfaces you can use in a MoI model, but also NURBS surfaces are a different kind of thing than polygons like for example 1 NURBS surface could be a really big complex curved wavy thing.

Of course eventually if you have enough surfaces you will run out of memory.

One thing you can do on heavier models to increase the display speed is to hide edges (display of the curved edges actually takes much of the redraw time on complex models), and also you can dial down the display mesh density to 25 degrees (the setting is under Options > View > Meshing parameters > Mesh angle), which will help conserve display memory on heavier models (at the expensive of a coarser looking display). But you have to get to a pretty complex quantity of stuff before that is necessary.

If you look through the gallery you can see some examples of some pretty detailed models, here is an example:
http://moi3d.com/gallery/viewitem.php?id=147

- Michael