FWIW, my PowerBook (1.33 GHz 12" with 768 MB RAM, 64 MB Go5200, 10.4.7) also runs SC4 much more slowly than it used to with Panther. I installed Panther on an external drive, and boot from that to run SC4. It runs much better under Panther. I'm hopeful that it is a machine specific problem, because when the Universal version of SC4 comes out, I want it to run well on my Intel iMac with Tiger.