I am not finding this FAQ to clear up a lot of my confusion regarding the various diffs that have been supplied stock in the USDM STi.
The 2007 apparently have a Torsen in the rear, as a new thing. I've noted a few posts talking about this like its a really significantly great improvement for some reason. But according to your FAQ, 2007 is the third model year for the USDM STi to have torsens in both front and rear - the 2004s had a suretrac unit in front.
As near as I can tell, it went like this:
2004 - Suretrac front, "mechanical" rear
2005 - "Helical" front, "mechanical" rear
2006 - "Helical" front, "mechanical" rear
2007 - "Helical" front, "Torsen" rear
Now, if really, for all intents and purposes, Torsen = helical = mechanical, I'd like to hear you explain why that is, but me and a lot of guys like me are still standing around out here wondering what the tiny little differences between these various units are, or where we can go to research it ourselves. There is a lot less general info about diffs out there than there is, say, suspension or forced induction concepts.