I understand your concerns, as balancing the cars proves to be a moving target.
The reason the Integra was backed down was because it was capable of accelerating and overall, being a few miles an hour faster than the other cars on almost every straight, on its own with no drafting help. Cars in the draft weren't able to keep up, and that was what was seen as being and unfair mechanical advantage. As far as tire wear is concerned, that appears to be a characteristic of the car. So unfortunately, I'm not entirely sure what to do about that. I would think that lowering the power would help that.
Now with the BMW, it gets a little weird. I have just played around with the Bimer around tonight's track with a few different setups at the 500pp mark as specified on the front, and here's what happened: I could not make that car do 57's around Silverstone, even in arcade mode. In fact, this is one of my slowest car. So for me, with the tuning guide that is on the master post, that I'm assuming and hoping that everyone is following, the BMW fits in with the field.
So now we're in an area where we would be balancing a car based how fast a driver is, rather than how fast the car may be. There is more than one BMW driver, and both drivers are not hitting the same, which is what makes this a bit of a sticky situation.