I like the M3 and the CS - I'm not a fan of the SLK.
I really liked the BMW. My pros on it were the really good torque, fast times and I liked the way the gear shift felt (although it was a tiny bit rubbery). It was a great car.
What I didn't like as much was the way the car was heavy and wobbly compared to the CS. I also felt that the BMWs were very, very common.
The CS has too many noises for my tastes - I keep torturing my dealer to button it down. The active suspension will help you get better track times - I do recommend it. I'm not sure the PCM (Porsche Communication Management) will help you with faster track times - unless you need the GPS to avoid getting lost at the track.
Finally - the noise of the CS is very much 'that Porsche noise' from the Boxer engine. I love the sound of it when I'm pushing the gas pedal down hard or when I'm blipping the throttle. It has that racecar heritage.
I love my car. It's solid on the track. It goes fast enough for me. But you have to decide for yourself. When you're spending this kind of cash - you have to be certain.
D.