Utility
The Impala will quite certainly prove handier than the Mazda MAZDA6 for those of you with frequent child-cargo.
Performance
Regarding horsepower, the Chevrolet Impala packs quite a punch and will knock the Mazda MAZDA6 down a few rungs. On the other hand, note that high horsepower engines often command higher insurance premiums.
Dimensions
The Chevrolet Impala's tank is about the same size as the Mazda MAZDA6's, though the Mazda MAZDA6's is a tad bigger.
The Mazda MAZDA6 and the Chevrolet Impala compete for the same parking spaces.
Cost
The destination charge is a standard charge for transporting the vehicle from its point of origin to the dealer. It costs almost the same to get the Mazda to the dealership as the Chevrolet Impala.
As far as MSRP, the Chevrolet Impala costs almost as much as the Mazda MAZDA6 (though the Mazda MAZDA6 is a tad cheaper).
Handling
With their comparable turning radii, the Mazda MAZDA6 and the Chevrolet likely handle approximately the same into and out of tight spots.
Drivetrain
The Mazda MAZDA6's engine is substantially smaller than the Chevrolet Impala's. Keep in mind that a smaller engine usually has to work a little harder; on the other hand, smaller engines typically get better gas mileage.
Torque is roughly equivalent to acceleration, and in this respect, the Chevrolet Impala is significantly more powerful than the MAZDA6.
Torque equals pickup, and the Chevrolet Impala will have picked up and gone by the time the Mazda MAZDA6 finally gets moving.
Comfort
The Impala is not particularly more spacious for your passengers than the Mazda.
Warranty
The Mazda MAZDA6 and the Chevrolet Impala have the same basic warranty.