Well...lets compare the Z8 to the....SL55...that will be a fun comparison. 5.5 liter supercharged V8 producing around 492 horsepower. 0-60 in 4.3 seconds. That would be very fun.

Anyhow...BMW I think should stick to motorcycles. I love their motorcycles...amazing...reliable...shaft driven..boxer. BMW Automobiles on the other hand really don't appeal to me. It's like comparing a TAG Heuer to a Rolex...you pay a decent amount more for the Rolex, but you get a heavy durable watch without a quartz movement. BMW's first car was a copy of the Austin Dixie.
BMW's just don't seem as solid and "beatable" as Mercedes. And they definately don't have the history of reliability. 4N, I'll race you in my 240D 4 speed...let me come to your house a bit earlier and "inspect" some stuff under the hood while you wait patiently inside your home