Hi TheEagle!
The file preferences.xml was renamed to defaults.xml (already some time ago, sorry for that wiki entry not having been up to date, I have changed that now).
About that multithreading thing:
I have tried all modes withour any problems but without much gain either. I did so because I did NOT read that wiki article before! Yes, that sounds SCARY!
I haven't heard of anyone saying that this setting had caused any harm to their computer, but maybe this is because they are unable to write since they tried (explosion, fire...).
Maybe someone else here can clarify; that wiki entry may have been written at times when that feature was still experimental or something.
Ciao,
Adrian