I'd agree completely with K-L.

I started with a MacMini 1.5Ghz to try out MorphOS (although I had tried it before on an Efika pre 2010) as it was the easiest way to play around with it, but although I still have the MacMini my main MorphOS machine is a G5 Quad simply as it is so much faster which makes modern web browsing a bit faster.

Don't get me wrong the G4's (I also have a Powerbook) can do it, but the G5 is just so much smoother. My MacMini also tends to get the fan spinning as the CPU load goes up and I get worried it will overheat, although that is more to do with games and intensive webpages.