How can I tell what gears are in my '06? It's a 6 speed. I have looked all over the place and can't seem to find any sort of markings that would show this.

use this for reference, if you have a stock 6 speed C6 then it is the M6 w 3.42 gears for example. go down a few lines until you get to the options listed

http://xse.com/leres/ss/calculator.html

The build sheet list might list it.