I noticed an extreme difference going from 133 to 533. Could not compare to a jump from 400 to 533. But, before I was going 16 internal clock cycles for each external cycle. I doubt that more than 50% of my clock cycles were being used. Using Poser 4, I've noticed that a render of 19 objects 7 of which were hi-rez textured Vicky 2's each with hair took just a few minutes. Wouldn't have tried that before. Extraneous factors that were involved: Doubled the system RAM to 1GB. Greatly reduced the swap time. While swapping the computer is over 1000 times slower than accessing RAM. I believe that increasing the RAM was more important than the FSB. But if you have the chance, go to 533. It will probably be considered lame in two years but 400 will be an absolute dinosaur.