Hi OutlawNut, below is a link to an Audioholic's article on speaker cable, it's very informative.
http://www.audioholics.com/education/cables/speaker-cable-gauge
If I may add; if it were me, and I had nice equipment as you do.
I'd use the same 4 conductor wire you've mentioned, except in-wall rated CL-2 14 and tie them together. By doubling them up it increases the gauge to around 11 AWG for the fronts.
Though I would use your idea for the rear surrounds. IMHO
As for CL-2 or CL-3 rated wire, if the work is being inspected you'll fail, without it.
If and when you go to sell your house, you will have to take it out.