Do your research on an actual detailing forum instead of on here, if you want to get accurate and thorough information. If you take the word of the Porter Cable voters without further information, you're being sold an orange when you asked for an apple.
You need to consider your use case before just plopping down cash for a tool; the PCXP isn't a bad tool, but it is an 8mm orbit machine whereas you were asking about 21mm polishers. Two totally different worlds.
For serious paint correction a 21 will be significantly more efficient, but also is limited when it comes to the ability to do panel edge work, and you won't be able to swap smaller backing plates on it (5-6" are the only options you have). The 8mm orbit tool is a bit of a jack-of-all-trades, master-of-few tool in that you can put lots of different sized backing plates on it down to 2-3", but it won't be as efficient at heavy paint correction as a large stroke tool.
So, are you looking to only own one polisher ever, or would you consider building out a suite of polishing tools over time as your needs develop and grow? How serious are you about this hobby?
And as far as the large stroke tools are concerned, I am admittedly a bit biased toward Rupes since they not only originated the category (the Torq and other brands are mostly Chinese knock-offs) and are now USA made (previously they were all Italian imports, but now made in a factory in Colorado), they also have wide repair parts availability and technical support should you need it. Just my $0.02.
