Do you have OEM 18" or 19" wheels? I'm asking because the OEM 18" tires start off with 9.5/32" F and 8.5/32" R of tread whereas the OEM 19" start with 8.5/32" F and R of tread.
Your current tread depth is approximately 5-6/32". Rears definitely wear faster than the fronts. Have you had the alignment checked? A poor alignment can result in severe treadwear. For only 2300 miles I'd say your treadwear rate is a little bit excessive. If most of your mileage is due to highway commuting, which I think it is based on your orig post, then I'd suggest getting your alignment checked. Otherwise it sounds like you are having a lot of fun with the car...