I ran up 16,000 miles on my Focus before rotating. I did not measure the tread depth, but just looking at them, I figure I had used up about 2/3d's of the tread on the front tires, while the backs had too little used to notice. I'd guess the fronts would have hit the wear bars at around 22-24k miles. I'm expecting to get about 40k out of them, and I drive it like I stole it.
This a front-driver, so it eats up front tires much faster than a RWD car, I find that, even without rotations, a front-engine RWD car is much more balanced about treadwear, unless you have a high hp car and use the power.
I don't know how spirited your driving is, but I find that treadware is very similar among different tires for me, simply because I break the harder compound tires lose more often. On my Impala, which is the only car I've worn multiple sets of tires out with, I average about 28k miles per set, with treadwear ratings ranging from 280-400. I often do powerslides with that car though. I think the GSD3 would actually give me longer life, but it does not come in the stock size. If I keep the car long enough to go through the current set of Kumho 712s, I'll be looking at the 255/45-17 GSD3, which is a bit shorter than the 50 series stocker.