Depends on how well the models are built. Often, a 20000 poly model would look just as good and detailed at 10000. I can't seem to find what the official poly limit is, but I know its a good range. Look at some of the good stuff in the showcases, probably Showcase II. If you know your stuff, you could pull off awesome environments and not even hit the poly limit. The difficulty in building a highly detailed world is FPS. There are tricks to lower that though. Somewhere in "game play & game design" there is a thread, probably 2-3 months old, that I started asking about the best way to achieve the best possible framerate.