I answered my own question. Stock appears to be 70%...or at least that is what is inscribed in the windows.....
Anyway...I got my rear and hatch windows professionally tinted today. I went with 18%.... which was one of the in-stock choices and I am extremely happy with it. I went over to PA to get it done which was only a 35 minute ride (from NJ). I had a choice of a tint with a 3 year waranty for $$150 or one with a lifetime warranty with garunteed no fading, no bubbling, or no delamination ever....for $225. I went with the higher quality film. The website of the film manufacturer is
www.Suntekfilms.com.
One other thing. To date I have never seen another Sonic on the road until today when I went inside the Tinting guys shop...there was a Blue Topaz Hatchback LTZ sitting right there and looking very good.
Key1