Cost
The destination charge is a standard charge for transporting the vehicle from its point of origin to the dealer. The BMW Z4 is considerably cheaper to get to the dealership than the Porsche Boxster.
The Porsche Boxster isn't much more expensive than the BMW Z4 when it comes to MSRP.
Utility
The Porsche Boxster and the Z4 can accommodate the same number of passengers.
Comfort
While the front cabin in the Z4 offers a bit more head room than the Porsche, there frankly isn't much of a difference.
Dimensions
The BMW Z4 is tremendously heavier than the Porsche Boxster.
Your wallet will hurt more every time you fill up the Porsche Boxster than the BMW Z4 because of its bigger tank.
The BMW Z4 and the Porsche Boxster compete for the same parking spaces.
Performance
With that kind of horsepower, both the Porsche Boxster and the BMW Z4 are true speedsters.
Handling
With their similar turning circles, the BMW Z4 and the Porsche Boxster most definitely handle approximately the same into and out of tight spots.
Drivetrain
The Boxster and the BMW Z4 have similar-sized engines, with a slight advantage to the BMW Z4.
Warranty
The BMW Z4 and the Porsche have the same basic warranty.