jval, it has already been reported by some that the numbers of ray hits and misses are the same in both Bryce4 and Bryce5 renders, on both the Mac and the PC (read my first post). This implies that the render options are the same in all cases. Refering to your earlier point, it is indeed possible that the programmers have coded Bryce to take advantage of some aspect of the Mac system. In itself, I have no problem with that. But if that optimised coding for the Mac is what is causing ten percent slower times on the PC, then I feel it's something worth talking about.