Stock has nothing to do with how hard the car is driven. These cars are autocrossed every day completely stock. Buy the absolute newest, lowest mileage, and unmodified vehicle you can afford.
In the last 2 years in just boost leaks and repairs alone I'm in 3500+ on my 95k mile 2011 WRX. It's also ragged out pretty good, needs the timing belt, water pump, clutch and suspension done soon. With BMW you've got great companies like bav auto. Closest we have is rock auto and even it can be expensive.
The 6 speed on the sti is nice. However day to day on the street I doubt you'll ever notice its advantages really. It does have a character and the limited slip diffs really shine in low grip situations. But good tire selection makes a larger difference.
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