This post is getting very interesting. I would love to have had the 89 tooth rear on my 2012 RSS. It would be like when the 80's model fox body mustangs were switching from the 2.73 and 3.08 gearing to something like a 3.73 or 4.10. It would really wake up that 225 hp 5.0 engine. Good luck with your changes, and report how things work out.