Utility
The BMW 328 will most definitely prove friendlier than the Porsche Cayman S for those of you with frequent child-cargo.
Performance
With that kind of horsepower, the Porsche Cayman S is a true sports car.
As far as horsepower, the Porsche Cayman S packs quite a wallop and will knock the BMW 328 down a few rungs. However, keep in mind that high horsepower engines often command higher insurance premiums.
Dimensions
The BMW's tank is almost the same size as the Porsche Cayman S's, though the Porsche's is a little larger.
Cost
The destination charge is a standard charge for transporting the vehicle from its point of origin to the dealer. The BMW 328 is substantially cheaper to get to the dealership than the Porsche.
With respect to MSRP, the BMW costs tremendously less than the Porsche Cayman S.
Warranty
The Porsche Cayman S and the 328 have the same basic warranty.