8 Gauge Speaker Cable

Hey. I recently moved to a new house and just finished ripping out a closet to make my audio room bigger. :-) I want to run my rear speaker cable through the ceiling and behind the wall I haven't put up yet.

1) Is this a good idea? There is nothing up there now except some plumbing. The outlet power lines are 6-8 feet from where I'm running the speaker wire.

2) Extrapolating from www.alphacore.com, in order to run 150 Watts 35 feet, I should use 8 gauge wire or larger. Does 8 gauge mean per terminal (+ or -), both terminals, the outer cover, or something altogether different?

3) Considering the cost of 8 gauge cable and that I only use the rear speakers 2-4 hours a week I'm considering using car audio grade wire and soldering the spades on myself. I used a blue/silver wire twisted into clear tubing in my car. It's $1.50 a foot on eBay. Anyone have experience with this? Good idea or am I missing something? Do I even need the braided wire or can I go with cheaper 8 gauge that isn't twisted?

Thanks!