Michael, perhaps you missed this edit to my previous post:

Just received this advice from SimLab:
"For simulation it is better to use an nurb based format like ACIS or STEP
while OBJ and 3DS will bring better material appearance.

ACIS and STEP will include inertia information, to get more accurate results.

So my suggestion to you is to try ACIS and STEP from MOI for simulation."
EDITED: 15 Feb by MGG942


So for simulation (and simple rendering) I've switched to STEP format and that seems fine for simulation and the level of rendering that I want.

Mike.