I think the Z4 is lighter due to the canvas top, so it might be a bit faster. I have nothing bad to say about the Z4, I'm one of the few that doesn't mind how they look, with the proper mods, it could look stunning.
I did look at it but didn't test drive it. It felt small compared to the SLK. The salesman kept pushing me to buy it and when I showed no interest, he was offering 14K off MSRP, that gave me a bad vibe, this car is either junk or there isn't interest, neither went well with me. And around here it was like the boxster a dime a dozen, and I wanted something new.
So I opted for the SLK, new design, head turner, performance, and hardtop, and the rest is history. Sorry I know that's probably not the answer you were looking for.
Actually, I was supposed to buy a Z4 but my uncle beat me to it so I went for an SLK350 because I didn't want to pass for a copycat. How childish is that?! Although I still believe the Z4 is a great car, I am absolutely sure I made the right choice. To me, the SLK is a sporty luxury car while the Z4 is more of a sportscar. I find it stiffer and less comfortable than the SLK. Also, the SLK is far more exclusive (at least in Montréal). I have seen less than 10 R-171s in the past two years while I see Z4s almost on a daily basis.
BTW, is your SLK Caspian blue like mine? The lighting on your piccie makes it hard for me to tell. What can I say, I am old and my eyes are not what they used to be!
Actually I wanted a Z4 when they first came out in 2003, I wanted it badly in Porsche Pastely Yellow and have it equipped with the whole Hamann Bodykit. Luckly enough I ended purchasing a Brutal,Mean and Sporty SLK55 thats much more fun out of the box.
But numbers really don't mean too much unless you test it for yourself. So what do you guys think? Has anyone actually come across any situations/experience??
Depending on the driver, the BMW could beat the MB or vice versus. Because the car's are closely matched, it becomes an issue of driver, tires, brakes (brake fade). I would look at when in the RPM range, which engine hits max torque. That will probably be the difference tracking the car.
Z4s feel really great on the road a bit on the stiff side, but i'll bet it'll be great for the track. the Z4M was actually a serious contender against the SLK...(or a Cayman S), but the torque of the 55 is simply too addictive.