Cube G4 450 with 768 MB RAM
Safari 3.2.1 Run 1: 70637.8 ms
Safari 3.2.1 Run 2: 35922.4 ms
Firefox 3.0.6: 25779.6 ms
Safari 4.0 Beta Run 1: 16029.8 ms
Safari 4.0 Beta Run 2: 12592.4 ms
MacBook Core 2 Duo 2.1 GHz with 2 GB RAM
Safari 3.2.1: 3739.6 ms
Firefox 3.0.6: 3440.0 ms
Safari 4.0 Beta: 867.0 ms
As you can see, with modern Intel dual-core machines, browsing was already fast. However, the new Safari 4.0 breathes new life into our old PowerPC Macs too.
Safari 4 is much faster than Safari 3 on Windows too. Unfortunately, the Windows version seems much more unstable, so I won't be using it until it gets some more updates.
Cube G4 1.7 GHz: 5648.8 ms
Nice. Now only if Adobe could speed up Flash.
By the way, this is what I get when I try to run the SunSpider bench on my Cube G4 450 with Firefox 18.104.22.168: