Most people just start throwing parts at a car to make it "faster" on the track. But really you need a plan - what specifically are you trying to change about how the car performs on the track? Tailor your parts to achieving your plan. Plus it is critical to ask yourself this basic question before modifying your car - are you getting 100% out of the car, 100% of the time? If somebody else could get into your car and go faster, don't spend a penny on it. Focus your mod dollars on upgrading the driver.
IMHO the stock suspension is basically great, except for the lack of front camber. Body roll is well controlled, it is not rolling onto the bump stops, it is pretty neutral and very predictable. Plus the street ride quality is excellent!
Personally if I was in your situation I would install the factory Performance Suspension package, keeping the original diameter front sway bar and installing the slightly larger rear M Sport sway bar. Unless you are racing your car competitively there is no reason to destroy your street comfort for an occasional track day. My bet is the BMW Performance suspension package is probably a great compromise and will be far more comfortable than any coil over setup.