I've been using Lumion (7.5) a lot lately to do fast renderings with heavy entourage because it's a beast of a program for this kind of thing, and it does it all in realtime*. Here is my recipe for exporting my models out of FormZ (8.5/6) so Lumion reads them correctly:
Export to FBX format (the image below indicates where the settings are located):
- Use Project Units, and set project units accordingly in Lumion. I work in imperial units, and Lumion defaults to metric.
- Export as Single Group. This assumes you have assigned colors or materials to your objects in fZ because that's the only thing Lumion cares about.
- Choose the Facetted option. I don't know if this matters or not, but I assumed Lumion wouldn't want parametric objects.
- Export Visible Layers Only. FYI This is a huge bonus that fZ has over SketchUp. What it does is self-explanatory.
- Click the Transformation button to bring up the Export Transformation dialog.
- Un-check Flip X
- Un-check Inverse Faces.
- Scale your model by 2.54 if you are using imperial units, because the FBX importer in Lumion thinks every model is in centimeters by default (you could also do this directly in Lumion after importing).
- Keep Fix Smooth Shading checked and set to 40, otherwise Lumion will try to over-smooth everything.
I didn't try to export textures because I do all my texturing in Lumion if possible. I would assume JPEG is the best option if you need materials. By default, fZ is set to TARGA format. Your mileage may vary.
This method worked perfectly for a complex terrain model with lots of additional detail covering a large site area. If you have questions, or a better way to do this, please do so in the comments below.
* if you have a beast of a computer to run it on.