I compared the stock Potenza S001 tires to my aftermarket tires. Both had been on the car for exactly 10k miles. It's very sad to see a stock tire nearly worn out after 10k miles, but a Contiental DWS06 all season performance tire lose only 0.8mm after 10k miles. I noticed that rolling resistance and noise are more of a factor at low speeds. At highway speeds, I'm not seeing any change in gas mileage or noise. At low speeds, I went from 55MPG to 50MPH on electric with aftermarket tires. Is that savings in gas mileage worth the extra money I spend on tires? I think not. I'd rather have a tire that performs better and is more cost efficient, while hearing a little bit more road noise. In addition, I can go into turns at higher speeds because the car isn't oversteering anymore. I'll never go back to the stock tires.
Here's my review of both after 10k miles: