Cost
The destination charge is a standard charge for transporting the vehicle from its point of origin to the dealer. The BMW 3 Series is considerably cheaper to get to the dealership than the Porsche.
The BMW 3 Series is tremendously less expensive than the Porsche when it comes to MSRP.
Utility
Neither the BMW 3 Series nor the Porsche 911 has a marked advantage when it comes to seating capacity.
Dimensions
The 3 Series is a bit more ponderous than the 911.
The BMW 3 Series's tank is approximately the same size as the Porsche's, though the Porsche's is slightly more capacious.
The Porsche 911 and the BMW 3 Series compete for the same parking spaces.
The 911's shorter wheelbase will likely give a nimbler feel in daily traffic. However, the 3 Series is likely to have a smoother, more stable ride.
Performance
With that kind of horsepower, the 911 is a veritable speedster.
Handling
The Porsche 911 has quite a bit bigger tires than the 3 Series. Keep in mind that wider tires could improve handling, while smaller tires may improve gas mileage.
Drivetrain
The Porsche 911's engine is substantially more sizeable than the 3 Series's. Keep in mind that more massive engines may use more gas than smaller ones.
The Porsche packs quite a wallop compared to the BMW 3 Series in terms of torque, which is roughly equivalent to acceleration.
The BMW 3 Series could learn a lesson or two from the Porsche as far as torque.
Overview
The Porsche 911 and the BMW 3 Series have the same basic warranty.