I also picked up some of this "speedwire" for my autodim/compass/temp mirror. Also looking for an overhead console. This stuff is normally used for stereo installs, but it was inexpensive and I thought would be perfect for this application. Probably a little overkill at 18ga wire, but I thought if I end up running anything that sends a little more current I'd be set.
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I wish I had some of that when I did my DIC install, that would have worked perfectly!
Also I like your idea of where you want to put your sub!