I guarantee you my P4 computer is not slow because of malware, I'm talking about a fresh install of XP; kind of a ridiculous assumption on your part when you have no idea about what kind of computer qualifications I have, don't you think? I could go into why you focusing on the numbers/specs game is a specious argument in this particular comparison, but I'll save that for another time.
I actually just took apart the P4 Wintel today, to donate the components as it has no further use to anyone in my family now that my grandma has moved out of the country. It's really just brutally slow, with a fresh install.
Speaking of which, maybe you should try that on your PowerBook as well. Junk software, files, and settings can accumulate on Macs too. And to my original point in the post you quoted, it all has to do with what you try to run on it. The P4 is nasty slow in my opinion just to use, but is really unusable because Firefox on XP and modern sites is a nightmare, whereas I can use PPC/Leopard optimized apps like Aurorafox on my PB (typing on my PowerBook right now in fact, running like a champ). If I were to use Firefox or any other recent build of modern software on the PB, it'd probably be just as bad of an experience as I have on XP with the P4, but the difference is, I can use optimized software for it. With the P4, it's a crap shoot.
EDIT: Of course, it's slower than an iPad. Even ignoring the fact that iOS is a very simplified and highly optimized operating system, the AX chips in Apple's iDevices are anywhere up to two times faster than the fastest laptop G4. They're faster than Pentiums too. They're just pretty darn fast period.