[lkchris]

The Porsche is certainly more dynamic and has a useful spare tire, which the Merc does not.

The Merc top probably rattles and most of your trunk space goes away when it's down. Doesn't have as much trunk space as the Boxster to begin with, but then the engine is a LOT more accessible for maintenance.

The Merc interior is head/shoulders above the Porsche in terms of quality. The Porsche is pretty chintzy. The way you rationalize that is to note the Porsche has an aluminum jack while the Merc jack is steel. Porsche means to keep weight down and chintzy is some of the result. In a similar vein, everything is optional on a Porsche and most of it is standard equipment on a Merc. An outside temp gauge has been standard on most Mercs since the 1980s.

You can buy a "red" air cleaner box and the Merc engine will sound better, but it's hard to beat the Porsche sound next to your left ear.

The Porsche has a brake wear sensor in all 8 pads. The Merc has one front and one rear.

An AMG SLK will likely leave a Boxster in the dust. A 280 SLK probably won't.