The G4 was amazingly power efficient, capable and highly cost effective for a time. The G5 was a poor stopgap that did suck power like a blow dryer. Most performance gains from the G5 were because of a higher clock and a faster bus. It had little in the way of true advantage over the G4. Intel did mop the floor with those chips, but only after Apple stopped using them.
The G4 was good for about one or two revisions. But then Motorola dropped the ball, the G4 was unable to scale to 500 mhz, and Apple had to cancel an entire Power Mac G4 line post announcement because Motorola was unable to produce, at all, the G4 chips they had promised Apple.
That's when it become pretty clear the G4 was not going to be maintainable. Apple got Motorola to mop up the mess, but the G4 was never really quite able to recover. The Pentium M came in shortly after and steamrolled the G4 on mobile.
The G4 was great for about a year, maybe two, but honestly, both IBM and Motorola (but mostly Motorola) totally repeatedly fumbled when it came to the PowerPC.
I eventually gave up and bought an Intel machine it was so bad. I was so gosh darn happy the day Apple announced the Intel transition. The writing had been on the wall for a while.
The promise of the G4 was pretty large, but Motorola time after time after time would make promises, and then totally and incompetently fail to deliver.
The advantages of the G5 were pretty clear: higher bus speed and faster memory. At the end of the day, you could make the G4 as fast as you wanted in theory, but you'd never be able to pipe the data in. It's why DDR memory or even PC-133 was pretty much ineffective on the G4. It was like putting a giant super factory at the end of a one lane dirt road. Yes, the G4 in
theory was fast, but in practice there was no way you'd get anywhere near getting enough data in for it to process.
Of course Motorola promised to fix the bus speed problems. And they fumbled. And they managed to get a whopping 33 mhz more. And then they fumbled some more. And then a year after Apple has given up and moved on they come out with a G4 with a decent clock speed and wonder why Apple moved on when it took them 5 years to fix the G4.
What a joke.