I don't see any analysis of the voltage regulation, line noise, or many specifics at all in that review to be honest. The Jonnyguru and HardOCP sites do thorough testing on the units before writing their reviews.
The different models in the same line being different qualities, are typically linked in with who actually manufactures the unit. If you get a GX550 make sure its one of the new ones model RS-550-ACAA-D3
The quick way to tell them apart is that the new model is Bronze 80+ and the old unit is Standard 80+
eta: one thing I don't like about the Jonnyguru reviews, are the Value and Aesthetics categories. Those categories can pull down the rating of a good unit, or boost the rating of a bad unit. Value is ephemeral, and aesthetics is in the eye of the beholder (plus a good portion of the time, its unseen)