Actually, for all the hype PPC Apples running OSX are pretty slow. And Flash and other multimedia suffers (until you're well above 1 Ghz or better yet you've got a G5).
I used to blame that on the processor, but I've been running MorphOS on a 933 Ghz 7455 and it runs most audio and video formats much faster (needs better flash apps though since currently the best way to view them is to download them and play them back via a media player).
A G3 running at 800 Mhz running standard Mac OS, the P3 probably would outperform it, but blame the OS (not Flash or the processor).
Anyone notice than even with massive Intel powered Mac's their game play still stinks? Quick hint guys -its not the hardware, its the operating system and attendant software