I imagine it'd be the same on PowerPC since the slow part there is the network speed, not the CPU. I bet the CPU is mostly idling on your Mini.
3 minutes sounds like ages. I've 73.9 days of stuff (24,221 songs) in iTunes here on my G5. It takes 14 seconds to load iTunes.
This talk of killing off PowerPC support in Safari is ridiculous. HTML5 isn't just about video, which is the only thing that really needs a faster CPU or GPU. All of the new HTML5 -webkit transitions and transforms work just fine on the 1Ghz G4 PowerMac I use as one of my website development machines. It's faster than some of the early Intel based Macs even.
Sure, it doesn't do 720p video well but neither do those Intel Macs either. My G4 PowerMac with a Radeon 9600 is better than my parent's Intel MacBook with GMA950 graphics.
The only thing Safari doesn't do in Apple's HTML5 demos is the 3D transforms because Safari presumably uses a Snow Leopard only library. It's not because PPC is slow or that the GPU is worse.
Apple would be killing off a lot of older machines with an Intel only version of Safari but then I guess we don't actually need it as most of the HTML5 features work already in Safari.
I'm not saying they should support PPC machines forever but Safari is a pretty important piece of software to stop support on if you're trying to push the HTML5 standard forward.