That does sound very strange. I had a Bryce 4 scene with 13 million polygons and it rendered fast even at 3000 x 2000 resolution on my P2 with 196 MB ram. It seems like Bryce treats terrain polygons differently and much more efficiently than other polygons such as trees. If that's really the case, then I'm starting to get worried about getting Bryce5.

"An Example is worth Ten Thousand Words"